Forums

Sega Master System / Mark III / Game Gear
SG-1000 / SC-3000 / SF-7000 / OMV
Home - Forums - Games - Scans - Maps - Cheats - Credits
Music - Videos - Development - Hacks - Translations - Homebrew

View topic - Simplest SEGA Mapper with off the shelf parts.

Reply to topic
Author Message
  • Joined: 24 Sep 2013
  • Posts: 138
Reply with quote
Simplest SEGA Mapper with off the shelf parts.
Post Posted: Sat Oct 17, 2020 9:56 pm
I've reworked my current mapper replacing the ATF16V8 PLDs, which require a dedicated programmer and are pretty much obsoleted, with a 512K Flash ROM that anyone can even order pre-programmed from some vendors (like Microchipdirect).

In essence the mapper needs the Flash ROM programmed with the attached .bin file, 5 10K resistors and 1 or 2 74HC573 latches, the circuit is as follows:



Connect the game ROM to the mapper as follows:

Game ROM       Mapper
A14            ROM-A14
A15            ROM-A15
A16            ROM-A16
A17            ROM-A17
A18            ROM-A18
!CE            !ROM_CE

Connect the rest of the game ROM pins to the SMS slot like a regular ROM.


I've ordered a few boards with this design. Further testing of this mapper required but it seems to work.
mapper-flash.png (37.18 KB)
mapper-flash.png
mapper.zip (1.93 KB)

  View user's profile Send private message Visit poster's website
  • Joined: 05 Nov 2014
  • Posts: 363
  • Location: Auckland - NZ
Reply with quote
Post Posted: Sun Oct 18, 2020 6:01 pm
Thats a cleaver approach. I like that!
  View user's profile Send private message
  • Joined: 05 Sep 2013
  • Posts: 2790
Reply with quote
Post Posted: Mon Oct 19, 2020 11:46 am
Would you mind explaining how are you using a ROM as a mapper?
Thanks! :)
  View user's profile Send private message Visit poster's website
  • Joined: 24 Sep 2013
  • Posts: 138
Reply with quote
Post Posted: Mon Oct 19, 2020 2:36 pm
sverx wrote
Would you mind explaining how are you using a ROM as a mapper?
Thanks! :)


From the SST39SF040 datasheet there is an option to drive the Data bus via changes on the Address bus without resetting !CE or !OE, making the ROM (chronogram on page 14) into an asynchronous programmable combinatorial circuit.

Also, is not the rom by itself doing all the work. You need the latch circuits and some pull-downs as well. The ROM just controls when to update and activate the address latches.
  View user's profile Send private message Visit poster's website
Reply to topic



Back to the top of this page

Back to SMS Power!