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 - Remaking the SEGA mapper clone out of discrete components

Reply to topic
Author Message
  • Joined: 24 Sep 2013
  • Posts: 140
Reply with quote
Remaking the SEGA mapper clone out of discrete components
Post Posted: Wed Jan 26, 2022 8:54 pm
Time ago I made a working SLOT 1/2 mapper using 16V8 PLDs and while it worked flawlessly the 16V8 PLDs are increasingly harder to come by and especially harder to flash due to 16V8 programmers being discontinued, so I want to replicate the PLD combinatory logic with off-the-shelf 74xx series.

So far I managed to replace the 2 16V8 PLDs with only 6 logic circuits, however I have a question about the ROM chip !CE line. While the original !CE used the following combinatorial equation:
!( !(A14 & A15) & CE & MREQ )

The current iteration uses the following one:
!( !(A14 & A15) & CE )

EDIT: (notice CE / MREQ are not negated, those signals come from inverters elsewhere in the circuit)

I was wondering if this is enough, since that would make the total bill of materials have just 6 logical circuits plus 1 or 2 latch ICs depending on whether the mapper would be SLOT2-only or SLOT1/2. This part is conveniently implemented using a single 74HC00 circuit, and I would want any changes (if needed) not to increase the IC count.

Once the doubts are resolved I'll finish the design and publish it here for all to use, like the previous design. Thanks in advance :)
  View user's profile Send private message Visit poster's website
  • Joined: 14 Aug 2000
  • Posts: 681
  • Location: Adelaide, Australia
Reply with quote
Remaking the SEGA mapper clone out of discrete components
Post Posted: Thu Jan 27, 2022 12:52 am
LGTM
  View user's profile Send private message
  • Joined: 24 Sep 2013
  • Posts: 140
Reply with quote
Post Posted: Thu Jan 27, 2022 9:11 pm
Mapper ready to be sent to fab. Will be doing some testing when it arrives. Meanwhile, I attach the schematic & gerbers to this post and the parts needed.


Qty  Value       Footprint
8    100nF       0805
1    Conn_02x20  Pin_Header_2x20_Pitch2.54mm
1    Conn_01x20  Pin_Header_1x20_Pitch2.54mm
5    10K         0805
2    74HC573     SOIC
2    74HC00      SOIC
3    74HC21      SOIC
1    74HC04      SOIC

mapper-module-v2-bw.pdf (83.83 KB)
Schematic
mapper-module-v2.2.zip (39.09 KB)
Gerber

  View user's profile Send private message Visit poster's website
  • Joined: 03 Mar 2022
  • Posts: 11
Reply with quote
Post Posted: Thu Mar 03, 2022 7:06 pm
Maybe the question is stupid, but for the #ROM_CE, why not directly using the #CE from the cartridge port?
  View user's profile Send private message
  • Joined: 26 Feb 2021
  • Posts: 87
Reply with quote
Post Posted: Mon Mar 07, 2022 8:28 pm
NeonMan wrote
Time ago I made a working SLOT 1/2 mapper using 16V8 PLDs and while it worked flawlessly the 16V8 PLDs are increasingly harder to come by and especially harder to flash due to 16V8 programmers being discontinued, so I want to replicate the PLD combinatory logic with off-the-shelf 74xx series.

Hello,
Microchip (Atmel) still manufactures PLDs (both in THT and SMT) in 2022 like ATF16V8 and ATF22V10.
As for programmers, here are some of the options supporting those PLDs in 2022:
- TL866 ($50)
- TOP3000 ($80)
- Of course pro stuff like Dataman, Xeltek, but not cheap at all
- Ultimately you have the DIY solutions
  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!