Help me upgrade from 64K to more on S1985-based MSX-2 computer

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By dhau

Paragon (1570)

dhau의 아바타

06-01-2007, 19:42

I think a while ago DamageX, our american MSX-friend, somehow upgraded amount of memory in his S1985-based MSX-2 system. I tried to find the thread with information, but failed. DamageX, can you please help me with info? We can chat via ICQ/GTalk/MSN/IRC or any other means you prefer. I would love to upgrade my revived Sony HB-F1 from 64K to 512K, or even more! Smile

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By DamageX

Master (217)

DamageX의 아바타

07-01-2007, 05:58

I found the thread for you, by searching for 628512 Smile

http://www.msx.org/forumtopic5569p15.html

I did stick a 74245 in there later on, to hold that one keyboard line low during reset so that the 512KB is always enabled. BTW, 512KB is the maximum when using the mapper in the S1985 since it only uses 5 bits. Let me know if you have any questions.

By dhau

Paragon (1570)

dhau의 아바타

07-01-2007, 12:45

Thank you very much, this project is in my pipeline now Smile

By msd

Paragon (1510)

msd의 아바타

07-01-2007, 16:43

Or insert a memory mapper in a free cartridge slot Tongue

By dhau

Paragon (1570)

dhau의 아바타

08-01-2007, 00:45

I do have 4MB memory mapper from Leonardo, but it's no fun at all. I like to play my game in one slot with gamemaster in the other.

By dhau

Paragon (1570)

dhau의 아바타

25-03-2009, 10:22

After years of contemplation, fear, anguish and regret, I decided to necroraise this topic from the chilly depths of interwebz.

DamageX: how exactly do you use 74245 to pull kbd line low on reset? Thanks Smile

By DamageX

Master (217)

DamageX의 아바타

26-03-2009, 01:11

I think I connected pin 19 /EN to the reset button. So normally the chip is tri-state, but when reset is pressed (tied to ground) the chip is enabled. Then if pins 18 and 1 are also grounded, pin 2 will be driven low during reset. So connect pin 2 to /X5 (keyboard input/config pin on s1985)

By RetroTechie

Paragon (1563)

RetroTechie의 아바타

26-03-2009, 18:35


I did stick a 74245 in there later on, to hold that one keyboard line low during reset so that the 512KB is always enabled. BTW, 512KB is the maximum when using the mapper in the S1985 since it only uses 5 bits.

I recall seeing a much simpler method somewhere (using a diode), but can't remember where. I checked S1985 datasheet, but it only says some keyboard inputs are latched at reset (to set some S1985 functions), but no example how to do that.

Then I thought of the Sony HB-G900AP, that rarely seen superimpose machine with S1985 engine inside (the more common HB-G900 (without -A) doesn't have S1985 engine, but countless 74LSxxx IC's inside). The schematic shows that the HB-G900A uses a 74LS670 IC to control mapper address lines MA18 (for 512K) and MA19 (for 1024K). But strangely enough, it uses another 74LS670 to control mapper address lines MA14~MA17 (for up to 256K). So that machine doesn't use the S1985 built-in mapper at all. Question So no clues there... Tongue

I'd try the simplest method first: a diode between suitable /RESET signal and keyboard input /X5 (S1985 pin 78). You should find somewhere an active-low reset signal (logic '0' during reset), for example /RESET signal that is fed to Z80. Connect that with /X5 keyboard input with an ordinary signal diode like 1N4148, BAT85 or similar. The marked side of the diode should be connected to the /RESET signal, so that it conducts current in /X5 -> /RESET direction. If you're lucky that's all you need to make S1985 output the MA18 address signal (for 512K mapper). If that works, a single 512K SRAM chip should finish the job.

Recently aquired a HB-F1 II myself. I very much like the look & feel of that machine, but unfortunately it isn't very 'solder-friendly' Crying Besides S1985 engine it's got a custom IC that I never saw before. I'm just guessing it serves as DRAM address multiplexer, and controller for that autofire / speed control stuff. 'custom IC' isn't a problem, but missing documentation (datasheet / schematic) is.

By DamageX

Master (217)

DamageX의 아바타

27-03-2009, 08:28

haha, I didn't try just using a diode. Shows how much experience I have with this sort of thing...

By Eugeny_Brychkov

Paragon (1232)

Eugeny_Brychkov의 아바타

24-04-2009, 13:16

Can you please explain what is a problem directly connecting memory to MA18/KBDIR? It seems for me that during reset cycle MA18/KBDIR will be driven low, thus higher 256K will be invisible during this time for the system. But eventually it will be released and again start functioning as MA18?

By Jipe

Paragon (1594)

Jipe의 아바타

24-04-2009, 18:39

on hb-f9 need a NPN transistor between diode and GND

B connect to B of transitor MUTE ( see schematic on hans otten )

C on x5 diode ----i

E on gnd

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