Memory Expansion in a MSX2 HB-F700S Project . . .

Hero (589)

22-10-2012, 22:54

Hello, I get a MSX2 HB-F700S, i´m just looking info about how mod the computer to a fully MSX2+ and other mods like some time ago i did with a HB-F9S with the help of some people of this forum.

Well, about memory expansion in the HB-F700S, i know S1985 allow expansion to 512K, but i´m looking for a memory mapper that can manage 4Mb, better than 1Mb, this memory mapper will be instaled internally in the computer, but i dont really sure if a 4Mb mapper is available or tested for this MSX2 model, and if the mapper could be manage SRAM, because i´m also planning install a Turbo Kit or Msx Super Turbo on the computer, then the memory should be SRAM and not DRAM, i think SIM memory is not an option. I´m still looking info about this but any help will be welcome.

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By overrich

Rookie (23)

23-10-2012, 00:49

Is there way to upgrade to 512K RAM on SONY Machine?
I saw some people upgrade 64K to 256K on thier SONY Machine

By Dhampird

Hero (589)

23-10-2012, 02:51

Hello, overrich, thanks for your reply in the other Multirom II post, i´m not an expert but about update SONY machines to 512K, if those SONY machines have the S-1985 engine (includes a 512 KB memory mapper inside) then you can update the RAM to 256K, and if you added an "extra circuit" (that should make S1985 output a mapper address line on the pin it shares with KBDIR signal) then you could get 512K, if the SONY machine have not the S-1985 engine you´ll need build an internal memory mapper to handle 512K or more, the HB-F700S have in-built S1985 but i´m looking a way to build a 1Mb or 4Mb Memory Mapper that can handle SRAM also; maybe another expert people could you tell more detailed info about this, like Retrotechie, try contact him.
With the help of experts brains in msx (people of this forum) i could install 512K SRAM on my HB-F9S (similar hardware like HB-F9P) and made another cool mods on it, please take a look at this post:

http://www.msx.org/forum/msx-talk/hardware/i-installed-512k-ram-internally-my-msx2-hb-f9s-works

If you need any diagram in big size about HB-F9S RAM expansion, let me know and i´ll send to your mail.

By Jipe

Paragon (1625)

23-10-2012, 15:19

on the HB700 the signal MA18 / KBDIR is not free because is used by the keyboard

By Dhampird

Hero (589)

23-10-2012, 17:02

Thanks for reply Jipe, then in HBF700 if MA18/ KBDIR is not free, then expansion to 512K (from S1985) not be possible? I´m looking for a external memory mapper to expand to 1Mb or 4Mb, i think i read about some people expand this machine up to 4Mb, i think you built time ago a memory mapper for use in this machine, do you still have any tested diagram?

By jltursan

Prophet (2619)

23-10-2012, 19:58

Quote:

on the HB700 the signal MA18 / KBDIR is not free because is used by the keyboard

Wasn't solved this issue when Retrotechie (and maybe you) recently helped to other user to upgrade its Sony HB-F1XD to 512K??

By usuario_msx2

Paladin (763)

23-10-2012, 20:16

jltursan wrote:

Quote:

on the HB700 the signal MA18 / KBDIR is not free because is used by the keyboard

Wasn't solved this issue when Retrotechie (and maybe you) recently helped to other user to upgrade its Sony HB-F1XD to 512K??

Problem is f500/f700/f900 model use ma18/kbdir(external keyboard). No problem with(integrated keyboard)sony model f9,xd,etc.

By Dhampird

Hero (589)

23-10-2012, 21:30

Thanks a lot for reply usuario_msx2, then, only option to update will be use a 1Mb internal memory mapper that handle 2 SRAM IC, like AS6C4008 (512K x8 SRAM)?, i´m wondering if the 1Mb Mapper could work ok with a Turbo Kit, like Msx Super Turbo or others.

Speculation: if ma18/kbdir is in use, will be possible generate that signals externally from S1985?, using any logic circuit, and then use original s1985 ma18/kbdir for external keyboard, and the new ma18/kbdir generated externally to can allow 512K memory upgrade?

By RetroTechie

Paragon (1563)

24-10-2012, 18:15

You'd basically have to build a memory mapper circuit inside the machine, and for >256KB, the HB-F700 won't help you. Unlike for example Philips NMS8250/55/80 machines, where you can pick up various signals from discrete logic IC's. You'd have the S1985 provide expanded address lines MA14-MA17 (for 256KB), and add mapper circuit to provide expanded address lines beyond that (for 512KB/1/2/4MB).

So you have a basic choice: 256KB max. with relatively simple wiring up (oh wait that's already in there! ), OR much more complicated mapper circuit to add (read: best to design a purpose-built pcb). I'm afraid I can't help you guys there as I don't remember expanding a HB-F700 to 4 MB before. I think I saw some circuit to control 4 MB*4 bit DRAMs (using /CAS-before-/RAS refresh) floating around the net, but have no idea where to find that (nor a clue whether it works at all & if so, how well). Alternatively you could use MK mapper circuit for 1/2/4 MB mappers which was published long ago. Look for "megamapper" from Digital KC. Ah there you go (look near the bottom of that page) - thx HansO!

By Dhampird

Hero (589)

25-10-2012, 06:38

Hello, thanks for reply Retrotechie, i have here a 1Mb mapper diagram from Jipe that i am studying and "seems" that can handle 2x512K SRAM IC´s, like AS6C4008 (512K x8 SRAM). I´m wondering if the "megamapper" from Digital KC could handle SRAM or only is designed for use with DRAM´s, better will be found compatible SRAM mapper, because after i´ll add Msx Super Turbo to the HB-F700, i dont know if those mappers could be a problem for Turbo kit purpose, the idea is to find "most compatible mapper" to allow Turbo Kit and SRAM can work without problems.
Thanks again for the info, as always and for good explanation.
Regards.

By Dhampird

Hero (589)

13-02-2013, 05:47

Finally, i get some extra time to build the mapper, thanks to Jipe info i built it like diagram picture show below, i added 4 SRAM sockets with their common points joined for future update to 2M, also another sockets for MSX-DOS 2 and F4 Register (not prepared yet).

I´m using now with the circuit 2XSRAM ic´s but when i tested the protoboard in HB-F700S worked only with 256K SRAM according memtest.com tool, then the mapper is not fully working at all, memtest should display 1M.

If you have any extra ideas will be welcome.

Here is the mapper circuit i followed:

and some install pictures: