Jrok's Mappy to Dig Dug 2 Guide

Background

This is something I just put together fairly quickly,  it should all be accurate & I re-tested, from my original notes, on another Mappy to confirm it still works. Let me know if there are any glaring omissions or errors.

To pre-empt anyone asking  'where are the ROMs ?'    try http://www.emuviews.com

Before you start

This conversion hack requires a certain level of technical ability so DO NOT attempt this without the correct tools and some experience in board level repair work.

Hardware

Mappy and Dig Dug 2 share very similar hardware, making conversion of a Mappy boardset to run dig dug2 fairly straightforward. Both video and CPU pcb's require some modification.

One significant part needed is a 56xx series custom IO controller from a Super Pacman board, it is used to replace one of the 58xx IOC's on Mappy.

Mappy uses two of the Namco 58xx I/O controllers, Dig dug 2 uses one 58xx and one 56xx. For reference superpac uses two 56xx.

Base Hardware Differences

The Real McCoy

To help protect the world against converted Mappy's being passed off as digdug 2's you can spot a 'bootleg' over an original in that all the original DD2's I've seen, 3 so far, have a large 40pin custom IC on the video PCB near the video out molex connector.

Click for a picture of a real Dig Dug 2 video PCB 

Rom Names & locations

Board Modifications

CPU Board Dig dug 2 adds an extra 8k of program ROM,  32k using 2 x 16k EPROMs over Mappy's 24k, using 3 x 8K EPROMs.  The address decoder at 2C on the CPU board needs to be modified to allow  the new program roms to appear at $8000-bfff and $c000-ffff in the memory  map, A13 needs to be supplied to the two 27128 EPROMs  A13 address lines, pin 26. CPU board modifications IC 2c,   74ls138 , pin 1 needs to be isolated from the PC board ( Address line A13 ) pin 1 should be bent away from the PC board, to avoid contact and jumpered to pin 16 of IC 2c. Two replacement Dig Dug 2 ROMs should be put into sockets 1B and 1D,  with pin 26 bent out, so it's outside the socket.  These pins should be jumpered together and tied to A13, pin 21 of the CPU 1A ( 6809 ). IO Controller,  the 58xx at location 4C needs to be replaced with a 56xx from a super pacman board.  IOC at location 4F, 58xx, remains the same.     Step 1: Cutting pin 1 from the CPU board     Bend pin 1 away from PC board and solder a jumper wire   Jumper wire on Pin 1 tied to pin 16 ( +5v )   ROM 1B & 1D pins 26 ( address line A13)  bent out from socket and jumpered together. ROM A13 tied to pin 21 on 6809 CPU location 1A, cpu address bus A13. CPU board Layout outlined areas areas are IC's to be replaced

Video Board Dig dug 2 supports twice the number of sprites using two 27128 GFX roms,  mappy having only two 2764's. Adding the additional sprite support to a mappy involves piggy backing on an unused half of a 74LS74 on the video PCB.  First some theory...  On the Mappy board location 4L - 74ls174 - controls sprite selection, it's uses a 5 bit value D2 - D6 for sprite number, low bits 0,1 are passed directly to custom IC 12xx. This data comes from buffered address bus 3, which RAM 2N shares. /VSET clocks the data from the databus  into 4L. The output 4L feeding the A12-A8 of the sprite ROMs 3L & 3N. To add the support for the extra sprites you use the spare side of ic 2C,  74ls74, 'D' input is bit 7 of the buffered data bus 3, clk is /VSET and output 1Q controls the A13, pin 26, of two 27128's in location 3N and 3M, these replace the two 2764's. ic 2C pins 1, 4 and 13 all jumpered together   pin 1 & 4 are connected pin 13  pin 2 connected to D7 - pin 9 IC 1N - 74LS245 pin 3 connected to /VSET - pin 9 of 4L - 74LS174 pin 5 connected to A13 - pin 26  IC 3N and 3M 4L pin 9   jumpered to pin 3 ic 2C 1N pin 9 jumpered to pin 2 ic 2C 3M & 3N pins 26 bent out of socket and connected together, also jumpered to pin 5 ic 2C Video Board Layout outlined areas areas are IC's to be replaced

Enhancements

In no particular order or timeframe...

1. Modify the original code to use the 58xx IOC instead of requiring the 56xx .
2. High-score save upgrade
3. Take a few more pictures

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