Cartridge Pinout (Sega Mega-Tech)
The Sega Mega-Tech cartridges have a different pinout than the Mega Drive. The A side is identical, but the B side is different.
You cannot just directly re-wire a Mega Drive game to the different pins, you will also require a ROM chip loaded with some header information too that presents the game title and descriptions to the Mega-Tech SMS Menu system.
Both Header and Game ROMs have their !E pin (chip enable when low) wired to !CE0.
The header ROM is typically a M27C256, with its !G pin (output enable when low) wired to the Header !OE pin.
The game ROM has its !G pin (output enable when low) wired to !CAS0.
That means when the system wants to read from the cartridge at all it first sets CE0 to low.
When it wants to read header information it sets the !Header OE to low, and !CAS0 to high.
When it wants to read the Game ROM it sets the !Header OE to high and !CAS0 to low.
Below are the pinouts of the Mega-Tech cartridge:
NOTE: Directions relate to the Mega-Tech side.
So, an audio as INPUT means the cartridge pin is an output to the Mega-Tech.
An address pin as OUTPUT means the Mega-Tech is outputting an address to the cartridge.
Pin | Direction | Designation | Description |
---|---|---|---|
A1 | Output | GND | |
A2 | Output | +5V | |
A3 | Output | Address Bit 8 | |
A4 | Output | Address Bit 11 | |
A5 | Output | Address Bit 7 | |
A6 | Output | Address Bit 12 | |
A7 | Output | Address Bit 6 | |
A8 | Output | Address Bit 13 | |
A9 | Output | Address Bit 5 | |
A10 | Output | Address Bit 14 | |
A11 | Output | Address Bit 4 | |
A12 | Output | Address Bit 15 | |
A13 | Output | Address Bit 3 | |
A14 | Output | Address Bit 16 | |
A15 | Output | Address Bit 2 | |
A16 | Output | Address Bit 17 | |
A17 | Output | Address Bit 1 | This is the first address bit, bit 0 is hardwired to low. |
A18 | Output | GND | |
A19 | Output / Input | Data Bit 7 | |
A20 | Output / Input | Data Bit 0 | |
A21 | Output / Input | Data Bit 8 | |
A22 | Output / Input | Data Bit 6 | |
A23 | Output / Input | Data Bit 1 | |
A24 | Output / Input | Data Bit 9 | |
A25 | Output / Input | Data Bit 5 | |
A26 | Output / Input | Data Bit 2 | |
A27 | Output / Input | Data Bit 10 | |
A28 | Output / Input | Data Bit 4 | |
A29 | Output / Input | Data Bit 3 | |
A30 | Output / Input | Data Bit 11 | |
A31 | Output | +5V | |
A32 | Output | GND | |
Pin | Direction | Designation | Description |
---|---|---|---|
B1 | Output | /VRES | System reset, from front panel switch. |
B2 | Output | /MRES | Master reset, from system start up. |
B3 | - | - | |
B4 | Output | Address Bit 9 | |
B5 | Output | Address Bit 10 | |
B6 | Output | Address Bit 18 | |
B7 | Output | Address Bit 19 | |
B8 | Output | Address Bit 20 | |
B9 | Output | Address Bit 21 | |
B10 | Output | Address Bit 22 | |
B11 | Output | Address Bit 23 | |
B12 | - | - | |
B13 | - | - | |
B14 | Output | Header !OE | Read from Header ROM. The !OE pin going to the header ROM |
B15 | - | - | |
B16 | - | - | |
B17 | - | - | |
B18 | Output | /AS | Address strobe, address on bus is currently valid and not changing. |
B19 | - | - | |
B20 | Input | /DTACK | Data acknowledge to 68K. |
B21 | - | - | |
B22 | Output / Input | Data Bit 15 | |
B23 | Output / Input | Data Bit 14 | |
B24 | Output / Input | Data Bit 13 | |
B25 | Output / Input | Data Bit 12 | |
B26 | Output | /CART | Pulled high in console, cartridge shorts to ground to indicate presence. |
B27 | Output | /CEO | Chip Enable for the cartridge. Normally low when accessing $000000-$3FFFFF region. When expension unit is present then low when accessing $400000-$7FFFFF. |
B28 | Output | /LWR | Lower byte WRite, the lower byte on the data lines should be written to the location in the address lines. |
B29 | Output | /UWR | Upper byte WRite, the upper byte on the data lines should be written to the location in the address lines. |
B30 | Input | /M3 | Pulled high in console, cartridge shorts to ground to indicate console should run in Mark 3 (Master System) mode. |
B31 | Output | /TIME | Set for r/w at/to $A13000-$A130FF, given the name suggests it might be for a real time clock in the cartridge. This would enable usage as a chip enable on a RTC, using fewer address lines or logic to that RTC. Used in Sonic 3 for SRAM. |
B32 | Output | /CAS0 | Read from Game ROM. Read or Write on $000000-$DFFFFF region. |
The Mega-Tech can read both the header info or game info.
Most games use a single Game ROM and a Header ROM:
And some games like After Burner also have an additional Paging Chip uses as a memory chip and sometimes game save.