Sega System 16B hardware notes (2003-01-12)
From Sega Retro
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This is a copy of an "unofficial" document containing original research, for use as a source on Sega Retro. This page likely exists for historical purposes - the contents should ideally be copy-edited and wikified to make better use of Sega Retro's software. Original source: http://cgfm2.emuviews.com/txt/s16tech.txt |
Sega System 16B hardware notes
by Charles MacDonald
WWW: http://cgfm2.emuviews.com
Unpublished work Copyright 2001, 2002, 2003 Charles MacDonald
This document is in a very preliminary state and is subject to change.
Most everything within has been tested and verified on a System 16 board,
but please be aware that my testing methods or interpretations of
results could be flawed. I can't guarantee that everything is 100% accurate.
What's new:
[01/12/03]
- Added information on ROM board 171-5704
- Added some ROM board connector pin assignments
[12/31/02]
- Added information on ROM boards 171-5358, 171-5797.
- Added information about tile and sprite banking.
- Added information on custom 68000 and MCUs.
- Added information about alternate background layers.
- Expanded description of sprite RAM attributes.
- Expanded description of configuration registers.
- Removed System 18 information (see s18tech.txt instead)
Initial release:
- Added information on sprite X coordinate range
- Added priority information
- Added wire harness pinout and I/O information
- Added information on Z80 sound command address
- Added more information about I/O area memory map
- Added information on sprite rendering
- Added info on foreground/background layers
Table of contents
1. Hardware overview
2. 68000 memory map
3. Sprites
4. Display timing and interrupts
5. Palette
6. Background and tile RAM
7. Text layer and text RAM
8. Layer priorities
9. Custom CPUs and MCUs
10. Wire harness pinout
11. Assistance needed
12. Credits and acknowledgements
13. Disclaimer
----------------------------------------------------------------------------
1. Hardware overview
----------------------------------------------------------------------------
The Sega System 16B hardware consists of the following:
68000 - 16-bit CPU used for game logic, inputs, video
Z80-B - 8-bit CPU used for sound playback
YM2151 - 8-channel 4-operator FM sound chip, for music & effects
uPD7759C - ADPCM sample player, used for voices & effects
It also has a socket for a 8751 microcontroller which seems to be present
in certain versions of some games.
I confirmed that the 68000 runs at 10MHz, but I don't know about the
other parts.
Sega custom IC's:
315-5195 - Unknown (connected to 68000, MCU)
315-5196 - Sprite generator
315-5197 - Tilemap generator
315-5213 - Unknown (PAL)
315-5214 - Unknown (PAL)
Memory:
2x TC5565APL-12 - 8Kx8 for the 68000
1x TMM2115BP-10 - 2Kx8 for the Z80-B
2x TMM2115BP-10 - 2Kx8 for the color RAM
2x TMM2115BP-10 - 2Kx8 text layer name table
2x HM65256BLSP-10 - 32Kx8 for the foreground/background layer name tables
2x TMM2018D-45 - 2Kx8 ?
4x TMM2018D-45 - 2Kx8 ?
If the System 16B hardware implements sprites anything like Galaxy Force II,
then of the latter six 2K RAMs listed, two are used with the high address
bit tied to ground to form 2Kx16 sprite RAM. The remaining four make up
two 512 entry by 12-bit word line buffers, which is probably for doing
double buffered sprite rendering. But apart from the sprite RAM, the rest
of this memory isn't accessible by the CPU.
ROM boards
The System 16B hardware has three types of boards which hold all of the
ROMs. Each one can implements sprite banking differently, and can optionally
have tile banking and extra hardware for software to use.
System 16B mainboard to ROM board connector pinout (incomplete):
CN4 A15 - /OE for region 1
CN4 B15 - /OE for region 2
CN4 B16 - /OE for region 3
CN2 A9 - Sprite bank bit 0 (CGB0)
CN2 B9 - Sprite bank bit 1 (CGB1)
CN2 A10 - Sprite bank bit 2 (CGB2)
CN2 B10 - Sprite bank bit 3 (CGB3)
CN1 A13 - Background tile index bit 12
CN4 A13 - /CE for all program ROMs (should be unique? 171-5358 only)
CN4 B13 - /LWR from 68000 (?)
ROM board descriptions
Board number: 171-5358
Used by: Shinobi, Tough Turf, etc.
Socket Type Description
A1 27512 68000 program code (odd)
A2 27512 68000 program code (odd)
A3 27512 68000 program code (odd)
A4 27512 68000 program code (even)
A5 27512 68000 program code (even)
A6 27512 68000 program code (even)
A7 27256 Z80 program code
A8 27256 uPD7759 samples
A9 27256 uPD7759 samples
A10 27256 uPD7759 samples
A11 27256 uPD7759 samples
B1 27512 Sprite data (odd, bank 0)
B2 27512 Sprite data (odd, bank 1)
B3 27512 Sprite data (odd, bank 2)
B4 27512 Sprite data (odd, bank 3)
B5 27512 Sprite data (even, bank 0)
B6 27512 Sprite data (even, bank 1)
B7 27512 Sprite data (even, bank 2)
B8 27512 Sprite data (even, bank 3)
B9 27512 Background tiles, bitplane 0
B10 27512 Background tiles, bitplane 1
B11 27512 Background tiles, bitplane 2
Region 0 is used for the chip enable for program ROMs A1 and A4.
Region 1 is used for the chip enable for program ROMs A2 and A5.
Region 2 is used for the chip enable for program ROMs A3 and A6.
Any unpopulated program ROM sockets return the prefetch value when read.
There are no provisions for tile banking, so bit 12 of each background tile
index has no special meaning.
The 4-bit sprite bank value taken from sprite RAM is used as a chip select
for each of the four sprite ROM banks:
CGB3 : 0= Enable bank 3, 1= Disable bank 3
CGB2 : 0= Enable bank 2, 1= Disable bank 2
CGB1 : 0= Enable bank 1, 1= Disable bank 1
CGB0 : 0= Enable bank 0, 1= Disable bank 0
If multiple banks are enabled there is a bus conflict and random data from
the enabled banks is shown.
If no banks are enabled it looks like a constant value is shown for every
group of four pixels, across the entire width of the display as no end
marker is being read. This repeats for the full height of all sprites
on-screen.
Board number: 171-5704
Used by: Tetris, Altered Beast, Cotton, etc.
Socket Type Description
A1 27010 Sprite data (odd, pair e)
A2 27010 Sprite data (odd, pair f)
A3 27010 Sprite data (odd, pair g)
A4 27010 Sprite data (odd, pair h)
A5 27010 68000 program code (odd)
A6 27010 68000 program code (odd)
A7 27010 68000 program code (even)
A8 27010 68000 program code (even)
A10 27256 Z80 program code
A11 27010 uPD7759 samples
A12 27010 uPD7759 samples
A13 27010 uPD7759 samples
A14 27010 Background tiles, bitplane 0 (banks 0,1)
A15 27010 Background tiles, bitplane 1 (banks 0,1)
A16 27010 Background tiles, bitplane 2 (banks 0,1)
B1 27010 Sprite data (odd, pair a)
B2 27010 Sprite data (odd, pair b)
B3 27010 Sprite data (odd, pair c)
B4 27010 Sprite data (odd, pair d)
B5 27010 Sprite data (even, pair a)
B6 27010 Sprite data (even, pair b)
B7 27010 Sprite data (even, pair c)
B8 27010 Sprite data (even, pair d)
B10 27010 Sprite data (even, pair e)
B11 27010 Sprite data (even, pair f)
B12 27010 Sprite data (even, pair g)
B13 27010 Sprite data (even, pair h)
B14 27010 Background tiles, bitplane 0 (banks 2,3)
B15 27010 Background tiles, bitplane 1 (banks 2,3)
B16 27010 Background tiles, bitplane 2 (banks 2,3)
Region 0 is used for the chip enable for program ROMs A5 and A7.
Region 1 is used for the chip enable for program ROMs A5 and A6.
Region 2 is used for tile banking.
Tile banking is implemented with a PLS153. The entire area of region 2 maps
to it's tile banking registers (The region 2 /OE signal is tied to it's
enable input). The PLS153 uses data bits 2-0 and address bit 1 when decoding
this area, to form a four byte region with two 3-bit registers mapped to
the odd bytes only:
$0001 - Bits 2-0 specify the tile bank for text layer tiles and background
tiles with bit 12 cleared.
$0003 - Bits 2-0 specify the tile bank for background tiles with bit 12 set.
This divides the tile ROMs into eight banks of 4096 tiles.
Reading any location in this range returns the prefetch value. The PLS153
initializes the tile banks to $07 on power-up.
Sprite banking
The 4-bit sprite bank value is shared between an address line of the ROM
sockets and a 74LS138 as follows:
CGB3 = Input C of 74LS138
CGB2 = Input B of 74LS138
CGB1 = Input A of 74LS138
CGB0 = A16 of each 27C010
Outputs 1Y0-1Y7 map directly to chip enables for sprite ROM pairs a-h.
This gives the following table of what ROMs and address offsets are
selected depending on the bank value used:
Bank bits ROMs enabled Offset selected
0 0 0 0 B1/B5 00000-0FFFF
0 0 0 1 B1/B5 10000-1FFFF
0 0 1 0 B2/B6 00000-0FFFF
0 0 1 1 B2/B6 10000-1FFFF
0 1 0 0 B3/B7 00000-0FFFF
0 1 0 1 B3/B7 10000-1FFFF
0 1 1 0 B4/B8 00000-0FFFF
0 1 1 1 B4/B8 10000-1FFFF
1 0 0 0 A1/B10 00000-0FFFF
1 0 0 1 A1/B10 10000-1FFFF
1 0 1 0 A2/B11 00000-0FFFF
1 0 1 1 A2/B11 10000-1FFFF
1 1 0 0 A3/B12 00000-0FFFF
1 1 0 1 A3/B12 10000-1FFFF
1 1 1 0 A4/B13 00000-0FFFF
1 1 1 1 A4/B13 10000-1FFFF
Some games such as Tetris do not have some or most of the sockets
populated, so bank values selecting those sockets are invalid. The sprite
data shown in this case looks the same way as when no banks are selected
for the 171-5358 board.
Board number: 171-5797
Used by: E-Swat, Golden Axe, etc.
Socket Type Description
A1 27020 68000 program code (odd)
A2 27020 68000 program code (even)
A11 27010 uPD7759 samples
A12 27010 uPD7759 samples
A13 27256 Z80 program code
B1 27020 Sprite data (odd, pair a)
B2 27020 Sprite data (odd, pair b)
B3 27020 Sprite data (odd, pair c)
B4 27020 Sprite data (even, pair a)
B5 27020 Sprite data (even, pair b)
B6 27020 Sprite data (even, pair c)
B7 27020 Sprite data (odd, pair d)
B8 27020 Sprite data (even, pair d)
B11 27020 Background tiles, bitplane 0
B12 27020 Background tiles, bitplane 1
B13 27020 Background tiles, bitplane 2
Region 0 provides the chip select for the program ROMs.
Region 1 provides the chip select for the tile bank and math chip hardware.
It's not clear what region 2 is used for.
Overview
The board has two main components, a PLS153 PAL used to implement tile
banking, and the 315-5248 / 315-5250 custom chips. These are part of a set
of chips used in several games:
315-5248 : Math chip (multiplication) in After Burner, Galaxy Force II
315-5249 : Math chip (division) in After Burner, Galaxy Force II
315-5250 : Math chip (compare) and Z80 sound command latch in After Burner
A 74LS139 is used to divide the memory map into four regions. The /OE signal
for region 1 enables the 74LS139, and 68K A13, A12 are used as select inputs.
1Y0 goes to the /CEx pins of the 315-5248, 1Y1 goes to the /MCCS pin of the
315-5250, and 1Y2 goes to pin 6 of the PLS153. 1Y3 is unconnected. This
gives the following offsets in region 1:
xx0000-xx0FFF : Multiplication registers (315-5248)
xx1000-xx1FFF : Compare registers (315-5250)
xx2000-xx2FFF : Tile banking (PLS153)
xx3000-xx3FFF : Unused (1Y3 is unconnected)
xx is the address specified by the base address and memory control registers
for region 1.
This 16K area is repeated througout the bank(s) allocated to region 1.
Offsets $0000-$0FFF hold the input and output registers for multiplication.
The 315-5248 can multiply two signed 16-bit numbers and provide a signed
32-bit result. It has four word sized registers that repeat throughout
the 4K space mapped to it:
Offset Read Write
$0000 - Return operand A Set operand A
$0002 - Return operand B Set operand B
$0004 - Return high 31-16 of result Set operand A
$0006 - Return bits 15-0 of result Set operand B
The result is always ready after updating the operand registers. Reading
the result in the opposite order, or multiple times, has no effect.
Writing to the operand registers in opposite order or multiple times also
does not change the expected result.
When writing in byte-sized units, writes to odd addresses have no effect
and writes to even addresses duplicate data in the LSB to the MSB. For
example:
move.b #$AB, $3E0006
move.b #$CD, $3E0007
This will set operand B to $ABAB, not $ABCD as expected. On the other hand,
byte reads from any address function normally.
Offsets $1000-$1FFF are for the internal registers of the 315-5250. Based
on the After Burner schematics, this chip handles comparisons. To the CPU
it looks like 24 word-sized registers that repeat throughout the 4K area
it's mapped to. I haven't done any testing with it at the moment.
Offsets $2000-$2FFF are for tile banking. The PLS153 uses data bits 2-0
and address bit 1 when decoding this area, to form a four byte region
with two 3-bit registers mapped to the odd bytes only:
$2001 - Bits 2-0 specify the tile bank for text layer tiles and background
tiles with bit 12 cleared.
$2003 - Bits 2-0 specify the tile bank for background tiles with bit 12 set.
This divides the tile ROMs into eight banks of 4096 tiles.
Reading any location in this range returns the prefetch value. The PLS153
initializes the tile banks to $07 on power-up.
Offsets $3000-3FFF are unused. Writes do nothing and reads return the
prefetch value.
Regarding region 2, E-Swat initializes the memory map like so:
Region 1 at $3E0000, 64K in size
Region 2 at $3F0000, 512K in size
This setup makes region 2 actually occupy $380000-$3FFFFF, with region 1
overlapping at $3E0000-$3EFFFF. E-Swat uses $3E2001 for tile banking only,
and doesn't try to use the math chip or any part of region 2.
Trying to access region 2 for the multiplication features of the math chip
seems to return the correct values on occassion, but mostly $FFFF is read
back. Maybe it's for expansion only, and without extra hardware conflicts
with the math chip.
Sprite banking
The 4-bit sprite bank value is used like so:
CGB3 = A17 of each 27C020
CGB2 = Select B1 input of 74LS139
CGB1 = Select A1 input of 74LS139
CGB0 = A16 of each 27C020
Outputs of the 74LS139: (which is always enabled)
1Y0 - /CE for sprite ROM sockets B1 and B4
1Y1 - /CE for sprite ROM sockets B2 and B5
1Y2 - /CE for sprite ROM sockets B3 and B6
1Y3 - /CE for sprite ROM sockets B7 and B8
This gives the following table of what ROMs and address offsets are
selected depending on the bank value used:
Bank bits ROMs enabled Offset selected
0 0 0 0 B1/B4 00000-0FFFF
0 0 0 1 B1/B4 10000-1FFFF
0 0 1 0 B2/B5 00000-0FFFF
0 0 1 1 B2/B5 10000-1FFFF
0 1 0 0 B3/B6 00000-0FFFF
0 1 0 1 B3/B6 10000-1FFFF
0 1 1 0 B7/B8 00000-0FFFF
0 1 1 1 B7/B8 10000-1FFFF
1 0 0 0 B1/B4 20000-2FFFF
1 0 0 1 B1/B4 30000-3FFFF
1 0 1 0 B2/B5 20000-2FFFF
1 0 1 1 B2/B5 30000-3FFFF
1 1 0 0 B3/B6 20000-2FFFF
1 1 0 1 B3/B6 30000-3FFFF
1 1 1 0 B7/B8 20000-2FFFF
1 1 1 1 B7/B8 30000-3FFFF
There are several games (E-Swat, Golden Axe) which do not have sockets
B7 and B8 populated, so bank values of 6/7 and E/F are invalid. The sprite
data shown in this case looks the same way as when no banks are selected
for the 171-5358 board.
PLS153N pinout
As used for tile banking in 171-5358, 171-5704 boards
1 = 68000 D0 20 = To tile ROM /OE (all)
2 = 68000 D1 19 = To tile ROM /CE (Low three ROMs)
3 = 68000 D2 18 = To tile ROM /CE (High three ROMs)
4 = From CN1 A13 17 = ?
5 = 68000 A1 16 = ?
6 = Enable input 15 = ?
7 = From CN4 B13 14 = ?
8 = (Unused) 13 = ?
9 = (Unused) 12 = ?
10 = Ground 11 = +5v
Pin 6 enables the PLS153N internal registers when held low.
Pin 4 is an input from bit 12 of the tilemap generator tile index.
Pin 7 is the /LWR signal from the 68000.
----------------------------------------------------------------------------
2. 68000 memory map
----------------------------------------------------------------------------
On power up, the first 64K of 68000 program ROM is mapped to the first 64K
of the 68000's address space. The memory map can be changed by software
through a set of configuration registers.
There are 32 of these write-only, byte sized registers mapped to odd
addresses within any 64K bank which has not been defined through the
registers themselves. They are mirrored every 64 bytes. Most games access
the registers at the following locations:
$FE00xx, $FF00xx, $C000xx
The first 16 do nothing except as follows:
$05 : 68000 is halted when any value is written.
$07 : Value written is sent to Z80 sound command latch, and an NMI signal
is sent to the Z80.
$09 : 68000 is repeatedly reset when any value is written.
The remaining 16 control the 68000 memory map:
$21 : Memory control for region 0
$23 : Bits 23-16 of region 0 base address
$25 : Memory control for region 1
$27 : Bits 23-16 of region 1 base address
$29 : Memory control for region 2
$2B : Bits 23-16 of region 2 base address
$2D : Memory control for region 3
$2F : Bits 23-16 of region 3 base address
$31 : Memory control for region 4
$33 : Bits 23-16 of region 4 base address
$35 : Memory control for region 5
$37 : Bits 23-16 of region 5 base address
$39 : Memory control for region 6
$3B : Bits 23-16 of region 6 base address
$3D : Memory control for region 7
$3F : Bits 23-16 of region 7 base address
Word access to even addresses is OK, the data must be in the LSB.
Riot City does this when setting up the memory map.
It would seem that for each region, any addresses that fall within the
defined memory range cause a unique chip enable signal to be generated.
The memory map is divided into 64K banks, though the memory control
register can allocate more banks for a particular region.
Regions 1 and 2 can be used for additional program ROMs or other hardware.
All games use the remaining regions as follows:
Region 0 - Program ROM
Region 3 - 68000 work RAM
Region 4 - Text/tile RAM
Region 5 - Object RAM
Region 6 - Color RAM
Region 7 - I/O area
The memory control register has the following layout:
MSB LSB
----mmss
s = These bits define how many 64K banks are allocated for a particular
region. Bits 20-16 of the base address specified are masked out
depending on the total size:
D0 D1 Size Mask
0 0 64K None ($FF0000)
0 1 128K $FE0000
1 0 512K $F80000
1 1 2MB $E00000
If whatever is mapped to a region is smaller than the number of banks
allocated for it, it is repeatedly mirrored throughout that region.
For example, allocating 2MB for object RAM results in the 2K of RAM
being mirrored 1024 times.
Tile/text RAM must be set to 128K or larger. Normally the hardware
places the tile RAM first and the text RAM at the next bank up. If the
size is 64K, then using an even bank only has the text RAM mapped to
it, and using on odd bank only has the tile RAM mapped to it.
m = The exact use is unknown. For all areas but text/tile RAM, having none
or either bit set has no effect, but having both set causes a lock-up.
For tile/text RAM only, both bits must be set. If not, the tile/text
RAM areas are not mapped to memory and a combination of the prefetch
value mixed with garbage data is returned from where the tile/text RAM
areas should be.
E-Swat sets bit 3 for the I/O area. This causes offsets $0000-0FFF and
$3000-$3FFF to have seemingly random data returned in the lower 4 bits
of data read from these areas. Maybe it enables more I/O ports.
- = Unknown, probably unused
All unmapped memory locations return the last word left on the data bus,
which is usually the opcode of the instruction following the one that read
memory, due to the prefetching. For example:
move.w #$330000, d0 ; Assume $33xxxx is unmapped
nop ; D0 = $4E71
A few addresses in the I/O area only use some bits of the data bus, and the
unused ones are set as shown above.
I/O information
The I/O area is 16K in size, mirrored repeatedly throughout the 64K segment
it's mapped to (e.g. Shinobi has the I/O area set to $C40000, and that
address is the same as $C44000 or $C48000). The 16K chunk is divided as so:
$0000-0FFF : Reads from any address return the next value off the data bus.
Writes to any address go to the miscellaneous control register.
(described later)
$1000-1FFF : Returns inputs 0, 1, 2, 3 in the LSB of each word, the MSB is
set to the next value off the data bus. Only A0 and A1 are
used, so the inputs are mirrored every four bytes.
$2000-2FFF : Returns DIP switches 0, 1 in the LSB of each word, the MSB is
set to the next value off the data bus. Only A0 is used, so the
DIP switches are mirrored every two bytes.
$3000-3FFF : Reads from any address return the next value off the data bus.
Shinobi writes to $C43007 once on startup and modifies bits 1
and 2 of $C43001 during gameplay, though I don't know what
this is for (or how these bits are mirrored).
The following is a description of various addresses in the I/O area. I'm
using the addresses that Shinobi accesses, but remember that the I/O area
can be mapped to different addresses and that some locations are mirrored
within their respective 4K areas.
For inputs 1-4, they all come from the wire harness. (CN1)
$C40001 : Miscellaneous control
D7 : ?
D6 : 1= Screen flip, 0= Normal screen display
D5 : 1= Display on, 0= Display off
D4 : ?
D3 : Output to lamp 2 (1= On, 0= Off)
D2 : Output to lamp 1 (1= On, 0= Off)
D1 : (Output to coin counter 2?)
D0 : Output to coin counter 1
When the screen is flipped through bit 6, the background and text layers
are flipped vertically and horizontally, and the sprites are flipped
horizontally but *not* vertically - so you'd have to swap the top and
bottom line values for each sprite to get them to display properly.
Bits 3 and 2 are for the lamps, Alien Syndrome uses them and the same
pins are assigned to lamps on the System 24 board.
I haven't been able to test bit 1, but the wire harness does allow for
two coin counters so in all likelihood this is the second one.
$C41001 : Input #1
D7 : Pin a
D6 : Pin Z
D5 : Pin Y
D4 : Pin X
D3 : Pin 23
D2 : Pin 22
D1 : Pin 21
D0 : Pin 20
$C41003 : Input #2
D7 : Pin 15
D6 : Pin 14
D5 : Pin 13
D4 : Pin 12
D3 : Pin 11
D2 : Pin 10
D1 : Pin 9
D0 : Pin 8
$C41005 : Input #3
D7 : Pin W
D6 : Pin V
D5 : Pin U
D4 : Pin T
D3 : Pin 19
D2 : Pin 18
D1 : Pin 17
D0 : Pin 16
$C41007 : Input #4
D7 : Pin S
D6 : Pin R
D5 : Pin P
D4 : Pin N
D3 : Pin M
D2 : Pin L
D1 : Pin K
D0 : Pin J
$C42001 : DIP switch #2
D7 : Switch 1 (0= ON, 1=OFF)
D6 : Switch 2 (0= ON, 1=OFF)
D5 : Switch 3 (0= ON, 1=OFF)
D4 : Switch 4 (0= ON, 1=OFF)
D3 : Switch 5 (0= ON, 1=OFF)
D2 : Switch 6 (0= ON, 1=OFF)
D1 : Switch 7 (0= ON, 1=OFF)
D0 : Switch 8 (0= ON, 1=OFF)
$C42003 : DIP switch #1
D7 : Switch 1 (0= ON, 1=OFF)
D6 : Switch 2 (0= ON, 1=OFF)
D5 : Switch 3 (0= ON, 1=OFF)
D4 : Switch 4 (0= ON, 1=OFF)
D3 : Switch 5 (0= ON, 1=OFF)
D2 : Switch 6 (0= ON, 1=OFF)
D1 : Switch 7 (0= ON, 1=OFF)
D0 : Switch 8 (0= ON, 1=OFF)
----------------------------------------------------------------------------
3. Sprites
----------------------------------------------------------------------------
General information
The System 16 sprites are fairly unique, while most video hardware
implements sprites as collections of tiles, the System 16 sprites are made
out of horizontal strips of graphics data that can span any height and
length.
A single sprite is defined by 16 bytes of sprite RAM. There is enough
space to define 128 sprites. Each entry has the following format:
MSB LSB
00: bbbbbbbbtttttttt
02: -------xxxxxxxxx
04: eh-----fpppppppp
06: aaaaaaaaaaaaaaaa
08: 1111bbbbppcccccc
0A: 000000vvvvvhhhhh
0C: ----------------
0E: mmmmmmmmmmmmmmmm
b : Bottom line of sprite
t : Top line of sprite
x : Sprite X position
e : 1= Hide this sprite and remaining sprites in list
h : 1= Hide this sprite
f : 1= Flip sprite horizontally
p : Sprite pitch (width, signed)
a : Start address of sprite graphics within 128K bank (word address)
1 : Either unused or more sprite bank select bits
b : Sprite bank select bits. (implementation dependant)
p : Sprite priority level
c : Sprite palette
0 : Sprite Y zoom information
v : Sprite Y zoom (0=normal, 31=50% reduction in height)
h : Sprite X zoom (0=normal, 31=50% reduction in width)
m : Sprite end address
- : Unused
The bottom and top line values define the sprite height. If the top value
is equal to or greater than the bottom value, the sprite is not displayed.
The sprite X position defines the starting location of the sprite. The
leftmost pixel of the screen is $00B6, and the rightmost is $1F5.
The two hide bits are used to disable individual sprites or to mark the
end of the sprite list, which prevents the current sprite and all following
sprites from being drawn.
The sprite pitch is a signed 8-bit number which is added to the sprite
bank address after each line is rendered. If the pitch is zero, then the
address never changes and the same graphics data is shown for every line.
A negative pitch is used to draw vertically flipped sprites, by setting
the start address to the last line of the sprite and stepping backwards
through the graphics data.
The start address specifies a word offset within a 128K bank. The address
is used internally by the sprite hardware and is not modified; the final
address used when the sprite has been rendered is written to the sprite
end address field (word 7) of the sprite RAM entry.
The sprite bank bits are output to the ROM board while a sprite is being
rendered. Hardware on the board uses the value to select what 128K bank
will be selected. See the section on ROM boards for more information.
The sprite priority level defines where sprites are placed between the
tile and text layers. See the section on priority for more information.
The sprite palette selects which one of 64 16-color palettes will be
use to draw the sprite. A palette of $3F is a special case and enables
shadow/hilight processing, see the palette section for more information.
The X and Y zoom values shrink the sprite by skipping pixels and lines
to cause up to a 50% reduction of height and width. Not all games use
this feature.
Word 7 of each entry is filled in by the sprite generator. It writes the
address of the last word it accessed within a sprite bank while rendering a
sprite. If the sprite has a pitch of zero, is hidden, or if the bottom line
is smaller than the top line, the start address is written as the end
address. (so no sprite data accessed)
The end address is only affected by the start address, height, pitch,
and Y zoom. The sprite X position, horizontal scaling and flip, and actual
graphics data from a bank has no effect on it.
In the same way bits 15-10 of word 5 of each entry are also filled in by
the sprite generator. Normally zero is written if the Y zoom value is zero,
and it changes based on a non-zero Y zoom value, the start address, pitch,
and top/bottom line values. I'm not sure what it is supposed to represent,
however. It may be the top few bits of a larger internal value, such as the
number of words skipped during zooming.
The sprite generator writes this information sometime after the active
display period, probably during vblank. If you write a value into the high
bits of the zoom word or the end address word, you can read the value back
until the sprite hardware renders sprites for this frame and fills in the
values itself.
Sprite data
Sprite pattern data is arranged as groups of words, within each word every
four bits defines one pixel, like so:
MSB LSB
aaaabbbbccccdddd
a = Pixel 0
b = Pixel 1
c = Pixel 2
d = Pixel 3
Some sprite pixel values have special meanings. Zero is transparent; such
pixels are not displayed. A value of 15 indicates an end marker - this is
also transparent, but additionally tells the sprite generator to stop
drawing the current line of a sprite. It's the end markers that define the
width of the sprite, which can vary on every line. I'll discuss the end
markers later on.
The pitch attribute for each sprite defines the value added to the start
address after a line of the sprite has been rendered. The value is a signed
byte, so $01 is 1 word, $FF is -1 word, and $00 really is zero, meaning the
address is never changed.
To draw vertically flipped sprites, the sprite pitch is made negative and
the address is set to the end of the sprite rather than the beginning.
The sprite generator will draw the last line of the sprite, then decrement
the address to point the next to last line, render it, and so on.
Sprite rendering
For normal sprites, the sprite generator adds the pitch to the base address
first, then starts reading words from the current bank and displays pixels
accordingly. If the last pixel of any four pixel group is set to $0F, it
stops rendering the sprite once the other pixels have been drawn. The pitch
is then added to the base address, and the process repeats for the next line.
This occurs on all lines that the sprite falls within.
For horizontally flipped sprites, the sprite generator starts reading words
from the base address plus an offset which is set to the pitch value. The
offset is decreased as each group of four pixels is displayed. If the first
pixel from any four pixel group is set to $0F, it stops rendering the sprite
once the other pixels have been drawn.
Sprite banks
Graphics data for the sprites is stored in banks that are 128K in size,
comprised of two 8-bit ROMs which are interleaved to form a 64K-word bank.
While the starting address in the sprite attributes is only 16 bits in size,
the sprite generator fetches data in units of one 16-bit word at a time,
so this is enough to span an entire 128K bank.
When the sprite generator accesses data from a bank, it's address into
the bank wraps at $FFFF back to zero. For example, a particularly large
sprite that had data at $FE80 would use data up to $FFFF, and then start
using data from $0000 onwards, of the *same* bank.
----------------------------------------------------------------------------
4. Display timing and interrupts
----------------------------------------------------------------------------
The video hardware generates a 262-line frame 60 times a second. Within
each frame, the active display period uses 224 lines and the remainder
is for vertical blanking and retrace.
At the start of line 223, a level 4 interrupt is generated which signifies
the beginning of the vertical blanking period. Since this happens on the
last line of the active display area, changes to the palette (or any other
kind of memory that alters the display) will still be visible.
The level 4 interrupt is automatically acknowledged by the video hardware.
If it is masked by SR when it is supposed to occur, the interrupt will be
generated as soon as SR is changed to permit it (even on a different
scanline or frame).
----------------------------------------------------------------------------
5. Palette
----------------------------------------------------------------------------
The output of the tilemap and sprite generators is combined by custom
hardware which determines priority between the various layers and ends
up with a 12-bit index into the 4K of color RAM.
Each 16-bit entry in color RAM has the following layout:
D15 : Shade hi/lo
D14 : Blue bit 0
D13 : Green bit 0
D12 : Red bit 0
D11 : Blue bit 4
D10 : Blue bit 3
D9 : Blue bit 2
D8 : Blue bit 1
D7 : Green bit 4
D6 : Green bit 3
D5 : Green bit 2
D4 : Green bit 1
D3 : Red bit 4
D2 : Red bit 3
D1 : Red bit 2
D0 : Red bit 1
Shadow / hilight mode is explained later. Up to 32768 colors can be
generated by the video hardware.
Palette usage:
Tiles from the text layer use color entries 0 to 63, divided into eight
8-color palettes.
Tiles from the foreground and background layers use color entries 0-1023,
divided into 128 8-color palettes.
Sprites use color entries 1024-2047, divided into 64 16-color palettes.
The backdrop color is shown behind all layers in the active display area
and is selected from palette entry #0. The remainder of the frame (meaning
overscan, vertical retrace, and vertical blank) is always shown as black.
If the display is turned off through bit 5 of $C40001, the affected lines
are also shown as black.
Palette flicker:
The color RAM has one data bus that is shared between the video hardware
and the CPU. If you try to read or write color RAM during the active
display period, the CPU access has precendence and the data it reads
or writes will select the color for the current pixel being displayed.
This does not occur outside of the active display period or when the
display is turned off, since color RAM is not being used.
Shadow / hilight processing:
If a sprite uses palette $3F, its' pixels with values 1 to 14 change how
underlying pixels from the background are shown (Values 0 and 15 are
still treated as transparent).
For each background pixel that is obscured by the sprite in question,
bit 15 of its' corresponding entry from color RAM is checked. If cleared,
the color is shown at half intensity. If set, the color is shown at double
intensity (or brightness, if that's a better way to describe it). The actual
sprite pixel is not shown at all. Most games leave bit 15 cleared in all
entries, so any sprite using palette $3F will create a shadow.
Sprite priority still works in the same way: if a shadow or hilight sprite
is behind one layer but in front of another, only the pixels behind the
sprite are affected. Shadow and hilight processing affects the backdrop
color, text layer, and both the foreground and background layers. It has no
effect on other sprites.
If two sprites overlap each other and one of them uses palette $3F, the last
one drawn (having the highest inter-sprite priority) will select how the
background is affected.
----------------------------------------------------------------------------
6. Background and tile RAM
----------------------------------------------------------------------------
The System 16 video hardware has two tiled backgrounds, which are called
the background and foreground. Each one is defined by a 128x64 virtual
name table, which is itself composed of four smaller 64x32 name tables.
The tile RAM holds sixteen 64x32 name tables which are selected through the
page selection registers (in text RAM). The four nibbles from the page
select register sets up the corresponding layer like so:
Name Table A Name Table B
Name Table C Name Table D
The advantage of this system is that the same subtables can be used to
save space while forming a larger virtual name table.
Each entry in tile RAM is one word. Some bits have several attributes mapped
to them, so the following layout shows each function for each bit:
MSB LSB
---nnnnnnnnnnnnn Tile index (0-8191)
---ccccccc------ Palette (0-127)
p--------------- Priority flag
-??------------- Unknown
The tile index picks one of 8192 tiles to display. Depending on the ROM
board used, some games implement tile banking by using bit 12 of the
tile index to select one of two banks, and the remaining bits as an offset
into a 4096-tile bank. See the section on ROM boards for more details.
The palette is associated with the tile index used. Some games have the
same graphics duplicated in the tile ROMs so they can be used with different
palettes.
The priority flag is explained in the priority section later on. It affects
the background tile's relation with sprites only, not with other layers.
Bits 14, 13 have no effect on the tile priority (with the sprites or
background), the tile colors, or the tile index. They could be unused.
----------------------------------------------------------------------------
7. Text layer and text RAM
----------------------------------------------------------------------------
Text RAM is used to store the name table data for the text layer, as well as
holding data for controlling the background and foreground layers. There is
4K of text RAM, and it is mapped 64K higher than the base of the tile RAM.
Text RAM layout:
$000-DFF : Text layer name table (64x28)
$E00-E7F : Unused
$E80-EFF : Unused, except for the following addresses:
$E80 : Foreground page select
$E82 : Background page select
$E84 : Foreground page select (alternate)
$E86 : Background page select (alternate)
$E90 : Foreground vertical scroll / column scroll enable
$E92 : Background vertical scroll / column scroll enable
$E94 : Foreground vertical scroll (alternate)
$E96 : Background vertical scroll (alternate)
$E98 : Foreground horizontal scroll / row scroll enable
$E9A : Background horizontal scroll / row scroll enable
$E9C : Foreground horizontal scroll (alternate)
$E9E : Background horizontal scroll (alternate)
$F00-F3F : Foreground column scroll table
$F40-F7F : Background column scroll table
$F80-FBF : Foreground row scroll table
$FC0-FFF : Background row scroll table
Text layer name table format:
MSB LSB
p???cccnnnnnnnnn
p : Priority. If 0, sprites with priority level 3 are shown over the text.
If 1, the text layer is shown over sprites regardless of priority.
c : Color palette
n : Tile index to use
? : Unknown
The name table is 64x28, but only 40x28 is shown. The viewable portion of
the name table starts at column 24 and goes to column 63, which maps to
screen columns 0 through 39.
Page select registers:
MSB LSB
aaaabbbbccccdddd
a : Page # for upper left page
b : Page # for upper right page
c : Page # for lower left page
d : Page # for lower right page
Vertical scroll / column scroll enable registers:
MSB LSB
e??????yyyyyyyyy
e : 1= Enable column-based scroll, 0= Enable whole screen vertical scroll
y : Scroll value for whole screen vertical scroll
? : Unknown
Horizontal scroll / row scroll enable registers:
MSB LSB
e?????xxxxxxxxxx
e : 1= Enable row-based horizontal scroll, 0= Enable whole screen horizontal
scroll
y : Scroll value for whole screen horizontal scroll
? : Unknown
Column scroll table format:
MSB LSB
???????yyyyyyyyy
y : Scroll value
? : Unknown
Row scroll table format:
MSB LSB
e?????xxxxxxxxxx
e : Enable alternate foreground or background layer for this row
x : Scroll value
? : Unknown
The row scroll works on units of 8 scanlines, the column scroll works on
units of 16 pixels (two tiles).
In column scroll mode, the columns aren't affected by horizontal scrolling
(either whole screen or row based), rather the vertical scroll value from
the column scroll table is applied to the display based on the current pair
of tiles being displayed (0 to 19). Each column is offset to the right by
the lower 3 bits of the horizontal scroll value, and the upper 7 bits select
an offset into the name table (this is almost identical to how the Sega
Genesis VDP handles column-based vertical scrolling).
For any entry in the row scroll table, having bit 15 set disables the
main foreground or background layer respectively and enables an alternate
foreground or background layer for that row only, which uses the page and
scroll values provided by the alternate layer registers. The alternate
layers cannot have row or column scrolling applied. They are shown in
replacement of the main layers, and are not additional ones (so still only
one foreground and one background plane are available)
This feature would be most useful for split screens and status screens,
which would otherwise need an entire background layer used exclusively for
them, or require use of raster effects.
----------------------------------------------------------------------------
8. Layer priorities
----------------------------------------------------------------------------
The priority order is as follows:
Highest Lowest
T1 > S3 > T0 > F1 > S2 > F0 > B1 > S1 > B0 > S0 > G
Key:
G = Backdrop color
S = Sprites (0-3)
B = Background layer (0-1)
F = Foreground layer (0-1)
T = Text layer (0-1)
The foreground, background, and text layer have two priority levels, while
sprites have four.
The tilemap priority settings only affect sprites; they cannot make tiles
from any layer appear over or under any others. (So the default order is
always T > F > B > G not counting sprites)
And likewise, the sprite priority settings only affect their relationship
with the tilemaps; the inter-sprite priority is not changed.
----------------------------------------------------------------------------
9. Custom CPUs and MCUs
----------------------------------------------------------------------------
Some System 16B games have a custom 68000 or Z80 that executes encrypted
program code. They may also have an Intel 8751 MCU.
The custom 68000 is a black epoxy block with a plastic shell around it.
The shell has a metal lid over the top which covers a small rectangular
recession, containing a regular CR2032-looking battery that is connected
to two wires that come from holes in either wall. A third wire is soldered
from the battery to the underside of the metal lid, meaning the battery
will be ripped out if the lid is removed too quickly or without enough
caution. The metal lid has the text "HITACHI FD1094", and a sticker
labeled "SEGA 315-0197". This number changes depnding on the game it's
used with, all encrypted games have different Sega part numbers.
The 68000 executes encrypted program code. It will not run unencrypted
code located in the ROM area or at higher addresses outside of the ROM
region (I tried tile RAM at $400000). The initial PC and SP values are
also encrypted, and the rest of the vector table is not encrypted.
The custom Z80 used in some versions of Shinobi is a black epoxy block
with a plastic shell around it. The shell has the text "NEC MC-8123B 651"
printed on the top, and a sticker labeled "SEGA 317-0054".
Inside the epoxy block is a 3 volt battery, the one I have was labeled
"MATSUSHITA ELECTRIC BR1125 LITHIUM". There's also a Fujitsu MB3771 power
supply monitor which switches between the battery or the regular 5 volt
source when the board is powered on. I think the drain on the battery
is fairly low, as the board I have is from 1986 and still works with
very infrequent usage.
The custom Z80 can be replaced with a regular Z80-B and unencrypted program
code from another version of Shinobi (but System 16B only, as the System 16A
sound hardware is a bit different), and the sound will work - I've read that
this has been done to fix boards that had no sound output but otherwise
worked OK. Presumably in this case the battery had died and the Z80 could
no longer decrypt the program code.
Here are my observations of how an 8751 MCU is used in Tough Turf:
The MCU reads the input ports (player 1, 2, service) and stores their values
into 68000 work RAM. It also accesses the Z80 sound command latch itself,
presumably taking the proper value to use from a location in work RAM.
It seems that if the first 32K-48K or so of ROM data is modified, the MCU
causes the hardware to lock up. Perhaps it compares a checksum of ROM to an
expected value, and hangs the machine if they don't match.
If the MCU is removed, the game functions normally except for missing
inputs and no sound.
----------------------------------------------------------------------------
10. Wire harness pinout
----------------------------------------------------------------------------
The System 16B boards use a non-JAMMA pinout that is also used with the
System 24 board. (and possibly others)
Component Side Pin # Solder Side
Ground 1 A Ground
Ground 2 B Ground
+5 Volts DC 3 C +5 Volts DC
+5 Volts DC 4 D +5 Volts DC
+12 Volts DC 5 E +12 Volts DC
Coin Meter 1 6 F Coin Meter 2
Lamp 1 7 H Lamp 2
Input 8 J Input
Input 9 K Input
Input 10 L Input
Input 11 M Input
Input 12 N Input
Input 13 P Input
Input 14 R Input
Input 15 S Input
Input 16 T Input
Input 17 U Input
Input 18 V Input
Input 19 W Input
Input 20 X Input
Input 21 Y Input
Input 22 Z Input
Input 23 a Input
Speaker (+) 24 b Speaker (-)
Monitor Red 25 c Monitor Green
Monitor Blue 26 d Composite Sync
Ground 27 e Ground
Ground 28 f Ground
Since the function of the various inputs is dependant on the game used,
I haven't listed any specifics (such as joystick or button use).
I modified the System 24 pinout found on spies.com for the above layout,
so thanks to whomever typed that up in the first place. ;)
----------------------------------------------------------------------------
11. Assistance needed
----------------------------------------------------------------------------
- Schematics for pre System-16, System 16A/16B or System 18 boards would be
greatly appreciated. :)
- Are there any other types of ROM boards beyond than the three I've
documented?
----------------------------------------------------------------------------
12. Credits and acknowledgements
----------------------------------------------------------------------------
- Sega for their great arcade games.
- Thierry Lescot and Nao for the System 16 emulator.
- The MAME team for the System 16/18 drivers.
- Sixtoe for maintaining the Sega Museum / System 16 website.
----------------------------------------------------------------------------
13. Disclaimer
----------------------------------------------------------------------------
If you use any information from this document, please credit me
(Charles MacDonald) and optionally provide a link to my webpage
(http://cgfm2.emuviews.com/) so interested parties can access it.
The credit text should be present in the accompanying documentation of
whatever project which used the information, or even in the program
itself (e.g. an about box).
Regarding distribution, you cannot put this document on another
website, nor link directly to it.