Control Pad (Mega Drive)

From Sega Retro

The Sega Mega Drive Control Pad is the official controller of the Sega Mega Drive (or Sega Genesis in North America). There are two main types of official Mega Drive control pad - "three button" and "six button" varieties, with the latter being brought in to replace the former towards the end of the system's lifespan (1994/1995). There are of course many other options as far as controllers go, including the Arcade Power Stick - a decendant of previous Sega joysticks. This article covers only the two basic pads.

Three button controllers are known officially as Control Pads in both North America and Europe, and SJ-3500s in Japan (following a system set up by the SG-1000). Six button controllers are known as SJ-6000s in Japan, 6 Button Arcade Pads in North America and Six Button Control Pads in Europe.

Mega Drive control pads are the logical progression from Master System control pads. Copying a system set up by Nintendo, the three button Mega Drive control pad adds, as the name suggests, an extra face button (or "Trigger" as it was initially called), C, to go with A, B and  START . A and B map to 1 and 2 on a Master System controller, while  START  eliminates the need for a pause button placed on the console unit itself. Six button pads add X, Y, Z and "MODE", meaning the total number of buttons is equal to that of the Super Nintendo.

The six button control pad would be used as a basis for the Sega Saturn Control Pad, though the MODE button would be scrapped in favour of an extra two shoulder buttons, L and R.

Mega Drive controllers are notable for being one of the first control pads to be ergonomically designed for the user's hands. Though improvements were made in the coming years, previous systems had cornered edges with their controllers, meaning they were often uncomfortable to hold after several hours of play. The Mega Drive controller is rounded, and has its buttons placed in easier to reach positions.

Variations

Control pads remained mostly the same across regions, but the colouring can determine the region and revision of the accessory.

Japan

SJ-3500

The first controller for the Sega Mega Drive, released in 1988. The A, B and C buttons are printed in red lettering and the  START  button is blue. The text at the top of the controller reads "Computer Video Game Control Pad".

SJ-6000 / Sega Club 6 button Jr

The Japanese 6-button controller. Again, the  START  button is blue, but the text is not coloured. It is, however, rendered in a serif font, as opposed to a sans-serif font used in international models. This would also be used in the Sega Saturn.

The Japanese model is smaller than its international counterparts. It is not the first controller to be made purposely smaller for a Japanese audience as the Sega Master System's Sports Pad also varies in size.

North America

Sega Genesis Control Pad (Model No. 1650)

Initial Sega Genesis three-button controllers had a white  START  button, with red coloured text. The arrows surrounding the D-Pad are also coloured red, and the printed text in the middle reads "Sega Genesis". These controllers match the Model 1 Genesis, and were distributed with the console during its early years.

Sega Genesis Control Pad (v2) (Model No. 1650)

When the Sega Genesis II rolled out, so were these updated controllers. The arrows were changed to white and the text was left black, much like the Genesis II console. The text "TRIGGER" was moved below the three buttons, and extra labels for A, B and C were added on top.

But it's not just the outside appearance which is different here. These models have an improved D-Pad mechanism, employing a metal ball-bearing for the pad to rock on. This prevented the wear which plagued the original design, which used a plastic nub for the rocking motion and would eventually wear down with frequent use. A minor addition is a little plastic lump on the B button, presumably to help users recognise where their right hand thumb was.

Sega Genesis Control Pad (v3) (Model No. 1650)

Though this controller appears to be identical to the above, it once again has an updated D-Pad. This was the first iteration of Sega's 2-Piece D-Pad mechanism, used in every official subsequent controller up to and including the Sega Saturn's. Rather than providing the rocking motion by a plastic nub or ball-bearing, there is a molded dome underneath the outside half of the D-Pad which allows the D-Pad to glide smoothly in a circle. This design was also plagued with wear like the first model, eventually resulting in all four directions being able to be pressed simultaneously.

Sega Genesis 6-Button Control Pad (MK-1653)

This is the standard, regular size 6-button controller for the Genesis. Devoid of colour (bar a grey  START  button), this controller debuted late into the Genesis' lifespan and uses the same D-Pad mechanism as the third three button control pad. It also bears the "SEGA" logo, rather than a Genesis one.

Sega Genesis 3 Control Pad (MK-1470)

This was the controller which was included with the Genesis 3 console. As the Genesis 3 was an economy model, manufacturer Majesco sourced them from a third-party manufacturer, based heavily on the Japanese SJ-6000 model. This became the most popular design and was simply rebranded with a different logo for each third-party company who decided to market it. It features six buttons, mode (black and moved to the front of the unit) and start (blue), and includes a switch to enable rapid-fire for all 6 buttons and slow motion via rapid pause.

Europe

Sega Mega Drive Control Pad

Almost identical to the second Sega Genesis three-button gamepad, the first European Mega Drive controller sports a white  START  button, the text "SEGA" and "Mega Drive Control Pad". Confusingly, the box uses a doctored image of a Sega Genesis controller, so the colour scheme does not match the acutal product.

Sega Mega Drive Control Pad II

The second model of Mega Drive control identical to the above varient, however now features a red  START  button instead of a white one, to correspond to the revised Sega Mega Drive II. This would become the most common Mega Drive controller, as far more Model IIs were sold in Europe than Model Is.

Sega Mega Drive Six Button Control Pad (MK-1653)

The European version of the 6-button control pad also contains a red start button, but is otherwise identical to the North American model.

Brazil

Asia

South Korea

Super Aladdin Boy Control Pad

The control pad that debuted along with Korea's Super Aladdin Boy is very similar to the first Japanese model. It contains a blue  START  button, red button text and the text "COMPUTER VIDEO GAME CONTROL PAD" printed on top. This is all rounded off with a Samsung logo in the middle.

Technical Information

3-button Control Pads

The chip inside the control pad is a 74HC157. This is a high-speed CMOS quad 2-line to 1-line multiplexer. Basically, how this works is there are two inputs ( A and B ) for every output ( Y ). There are four groups like this. There is one select signal for the whole chip. When the select signal is low, the output ( Y ) is the same as input A. When the select signal is high, the output Y is the same as input B. The pinout for the chip is as follows:

Pin 1 Select
Pin 2 1A
Pin 3 1B
Pin 4 1Y
Pin 5 2A
Pin 6 2B
Pin 7 2Y
Pin 8 Gnd
Pin 9 3Y
Pin 10 3B
Pin 11 3A
Pin 12 4Y
Pin 13 4B
Pin 14 4A
Pin 15 G (? must be low)
Pin 16 Vcc (+5V)

All the controls are done with switches. Up is a switch, Down is a switch, etc. Now, I will be referring to the output of these switches later on. The output is usually high when the switch isn't pressed. When the button is pushed, the output goes low. This is accomplished by connecting the output to +5V through a 10k resistor. The button is then attached between the output and ground. It looks like this:

    +5V -----/\/\/------+--------- Output
              10k       |
                        |
               /        |
  Ground -----/  -------+
             button
             (normally open)

The line numbers are determined as follows, looking straight at the plug on the front of the Genesis the numbers are:

	1 2 3 4 5
	 6 7 8 9
Line 1 Up output.
Line 2 Down output. These are the only two direct connections.
Line 3 Pin 4 of the chip. Output 1Y.
Line 4 Pin 7 of the chip. Output 2Y.
Line 5 This line carries in +5V. It is connected to the +5V bus line.
Line 6 (TL) Pin 9 of the chip. Output 3Y.
Line 7 (TH) Pin 1 of the chip. This carries in a select signal from the Genesis. This is a signal which varies rapidly and controls which input goes through the output
Line 8 Ground. This is connected to the Ground bus line.
Line 9 (TR) Pin 12 of the chip. Output 4Y.


Now for the chips pin connections:

Pin 1 Line 7 (select)
Pin 2 Ground (1A)
Pin 3 Left (1B)
Pin 4 Line 3 (1Y)
Pin 5 Ground (2A)
Pin 6 Right (2B)
Pin 7 Line 4 (2Y)
Pin 8 Ground (GND)
Pin 9 Line 6 (3Y)
Pin 10 Button B (3B)
Pin 11 Button A (3A)
Pin 12 Line 9 (4Y)
Pin 13 Button C (4B)
Pin 14 Start (4A)
Pin 15 Ground (G)
Pin 16 +5V (Vcc)

6-button gamepads

In order to maintain backwards-compatibility with existing games, the 6-button gamepad acts the same as the 3-button if the controller inputs are read by the program a maximum of four times per frame. Reading the 3-button gamepad takes two cycles (once with TH=1 to read Up, Down, Left, Right, B, and C; and once with TH=0 to read A and Start), and the 6-button gamepad allows this to occur twice. It then reports the state of the extra buttons when the TH line is changed after the fourth cycle.

The full controller state is read in 8 cycles:

Cycle TH out TR in TL in D3 in D2 in D1 in D0 in
1 HI C B Right Left Down Up
2 LO Start A 0 0 Down Up
3 HI C B Right Left Down Up
4 LO Start A 0 0 Down Up
5 HI C B Right Left Down Up
6 LO Start A 0 0 0 0
7 HI C B Mode X Y Z
8 LO Start A --- --- --- ---

Note: For the 8th cycle, '---' indicates "don't care". These values are all 1 on the 6-button controller, but may be mapped to other buttons on third-party controllers. Software expecting 6-button controllers should simply ignore these values. (6-button detection should be done on the 6th cycle, which presents four 0's on the D lines.)

The controller's internal counter automatically resets after the eighth cycle. It also resets if it doesn't detect a rising-edge (0 to 1) transition on the TH line within 1.5 ms, which ensures that most games that don't support the extra buttons won't read them accidentally.

Some games incorrectly read the controller more than twice per frame, which may cause them to read the wrong set of buttons. If the Mode button is held in while starting the Genesis console, the 6-button gamepad will disable the extra buttons and act identically to a 3-button gamepad. (That is, the controller's internal counter will reset after the first two cycles instead of after eight cycles.)


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