Repair & Schematics
Sega Mega-Tech Arcade

Cartridge Pinout (Sega Mega-Tech)

4min

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:

Cartridge connector pinout
Cartridge connector pinout


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.

Cartridge Examples

The Mega-Tech can read both the header info or game info.

Most games use a single Game ROM and a Header ROM:

Reproduction Game
Reproduction Game

Golden Axe
Golden Axe


And some games like After Burner also have an additional Paging Chip uses as a memory chip and sometimes game save.

After Burner
After Burner