Mega Drive Serial Port

Tools and docs for using a SEGA Mega Drive controller port in serial mode

Diagnostics Tool

When the ROM starts, it:

Enables Serial Mode on Port 2
Sets speed to 4800 bps
Receives data into a 2K buffer on hardware interrupt (can be configured to poll instead, but is not reliable at speeds greater than 1200 bps)
Send a continuous stream of 0123456789\n
Prints any received data to the screen.

Docker:

./docker-make

Linux (requires cmake & gendev):

make

Pin	Parallel Mode *	Serial Mode	I/O Reg Bit
1	Up		UP (D0)
2	Down		DOWN (D1)
3	Gnd / Left		LEFT (D2)
4	Gnd / Right		RIGHT (D3)
5	+5VDC	+5VDC
6	Button A / Button B	Tx	TL (D4)
7	Select
8	Gnd	Gnd
9	Start / Button C	Rx	TR (D5)

* Pins in parallel mode can have two interpretations, depending on if Select has been set low or high (L / H) from the console.

Looking directly at plug (Female 9-pin Type D)

-------------
\ 5 4 3 2 1 /
 \ 9 8 7 6 /
  ---------

From the datasheet:

Colour	Name	Type	Description
Black	GND	GND	Device ground supply pin.
Brown	CTS#	Input	Clear to Send Control input / Handshake signal.
Red	VCC	Output or input	Power Supply Output except for the TTL-232RG-VIPWE were this is an input and power is supplied by the application interface logic.
Orange	TXD	Output	Transmit Asynchronous Data output.
Yellow	RXD	Input	Receive Asynchronous Data input.
Green	RTS#	Output	Request To Send Control Output / Handshake signal.