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

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rhargreaves/mega-drive-serial-port

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Mega Drive Serial Port CircleCI GitHub release (latest by date)

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.

Build

Docker:

./docker-make

Linux (requires cmake & gendev):

make

Hardware

Controller Port Pinout

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.

Controller Plug

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

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

FTDI USB TTL Serial Cable

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.

Mappings

FTDI Cable Mega Drive Port Pin
Orange (TXD) 9 (Rx)
Yellow (RXD) 6 (Tx)
Black (GND) 8 (Gnd)