Sega Genesis/MegaDrive Expansion Port Pinout
This pinout is took a while to complete. As part of an effort to connect a Teradrive to a SegaCD unit, I had to trace the expansion port. This is it. Some pins are labelled by destination rather than signal, for example 87/315-5364. This means it runs to pin 87 of the IC 315-5364. Also, this refers only to the model 1 Genesis/MegaDrive. There may be minor differences in the model 2, for example the audio in the 2 does not require the patchcord, so I assume there's a small difference there.

Some of the pin names may sound a little odd, they're based on corresponding cartridge port pins. The majority of the pins on the expansion port, for example the data and address lines, connect to the same pins on the cartridge port. /C_OE is Cartridge Output Enable, which sounds a little odd on the expansion port, but I'm sure you'll adjust. If you have any additional info on this or the model 2 differences, please email me.

pinName
A01GND
A02NC
A03/C_OE
A04D00
A05D01
A06D02
A07D03
A08D04
A09D05
A10D06
A11D07
A12GND
A13D08
A14D09
A15D10
A16D11
A17D12
A18D13
A19D14
A20D15
A2187/315-5364
A22/LO_MEM
A2391/315-5364
A2486/315-5364
A2510/315-5309
A26+5v
A27NC
A28VCC IN*
A29Audio*
A30GND
pinName
B01GND
B0211/315-5309
B03A01
B04A02
B05A03
B06A04
B07A05
B08A06
B09A07
B10A08
B11A09
B12GND
B13A10
B14A11
B15A12
B16A13
B17A14
B18A15
B19A16
B20A17
B21/LDS
B22/UDSW
B23Cart B21*
B2485/315-5364
B2510/315-5309
B26+5v
B27NC
B28VCC IN*
B29Audio*
B30GND


* VCC IN - It appears the SGCD is capable of powering the main console through these pins. Power from them is routed directly to the console power switch through a pair of diodes.
* Cart B21 - This pin connects to the cartridge slot B21, function unknown.
* Audio - This is assumed functional, but is untested.



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