AX5904 WRAM control

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mightydidz
Posts: 30
Joined: Wed Jan 24, 2018 12:04 pm

AX5904 WRAM control

Post by mightydidz » Tue Oct 13, 2020 7:41 am

Guys, I'm searching infos on how MMC1 clone AX5904 controls WRAM.
I'd like to avoid salvaging boards, so using clone is interesting.
I'm wondering if a schematic is available to use AX5904 for SN, SO, SU, SX, SZ builds.
Does it have timing issue compared to Genuine MMC1?

krzysiobal
Posts: 790
Joined: Sun Jun 12, 2011 12:06 pm
Location: Poland

Re: AX5904 WRAM control

Post by krzysiobal » Tue Oct 13, 2020 12:43 pm

I've just checked and AX5904 ignores PRG RAM enable bit (RAM is always enabled).
Delay between rising edges of M2 and RAM+CE is 11ns and between falling edges is 16ns.

In comparision, MMC1B2 that I have has a delay between rising edge of M2 and RAM+CE around 78ns and between falling edges 8ns !!
Also, RAM is enabled by default (on power-up), wiki is wrong in that matter.
CH1=M2, CH2=RAM+CE, CPU-R/W=1, CPU-A=$6000, CPU-ROMSEL=1
CH1=M2, CH2=RAM+CE, CPU-R/W=1, CPU-A=$6000, CPU-ROMSEL=1

It means that AX5904 might cause troubles when no RAM delay circuit is present.
Last edited by krzysiobal on Tue Oct 13, 2020 1:32 pm, edited 1 time in total.

lidnariq
Posts: 9777
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Location: Seattle

Re: AX5904 WRAM control

Post by lidnariq » Tue Oct 13, 2020 12:52 pm

krzysiobal wrote:
Tue Oct 13, 2020 12:43 pm
Also, RAM is enabled by default (on power-up), wiki is wrong in that matter.
Isn't that what the page says?

krzysiobal
Posts: 790
Joined: Sun Jun 12, 2011 12:06 pm
Location: Poland

Re: AX5904 WRAM control

Post by krzysiobal » Tue Oct 13, 2020 1:33 pm

lidnariq wrote:
Tue Oct 13, 2020 12:52 pm
krzysiobal wrote:
Tue Oct 13, 2020 12:43 pm
Also, RAM is enabled by default (on power-up), wiki is wrong in that matter.
Isn't that what the page says?
Sorry, I'm blind :roll:

I had two AX5904's and both share the same behaviour.

I have another, nameless MMC1 clone and it is yet different - delay is even bigger than in original MMC1B2 but it still has RAM permanently enabled.
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mightydidz
Posts: 30
Joined: Wed Jan 24, 2018 12:04 pm

Re: AX5904 WRAM control

Post by mightydidz » Tue Oct 13, 2020 2:16 pm

Is it better to have WRAM always enabled or should I re-create WRAM+CE using M2+delay?
And what about the no RAM circuit? How can I safely deglitch this delay?
I've seen reproboard online that uses AX5904. Are they reliable?

krzysiobal
Posts: 790
Joined: Sun Jun 12, 2011 12:06 pm
Location: Poland

Re: AX5904 WRAM control

Post by krzysiobal » Tue Oct 13, 2020 2:17 pm

mightydidz wrote: You replied to my post mentioning wram is always enabled with AX5904, so using a simple inverter on +5v would do the trick?
I meant the protection bit $e000.5 does not have any effect (RAM can't be disabled, it is always enabled when accessing $6000-$7fff, just like in MMC1A), this should be not a problem because almost no game rely on it.
mightydidz wrote: I was also considering adding a pull up on SRAM-!ce to make sure it stays in standby while system is powered off.
Are you going to use 6264 or 62256 as SRAM?
* If 62256 then you need additional low-power inverter, which need to be battery powered aswell (just like here.
*If 6264 then do it just like they did on genuine MMC1 boards:
-> pull-down on WRAM+CE
-> WRAM-!CE and WRAM-!OE tied to gnd.
mightydidz wrote: I'm just concerned about this delay your mentioning compared to MMC1B2?
I'm not an expert with scope, but your comparing M2 and Wram+ce?
Correct me, but I dont see any Wram+ce on AX5904?
what about pin 6?
migtydidz wrote: Should I plan to add any capacitor on M2 to help deglitching?
Thanks for the help
If you plan to use 6264, just do it that way:

Code: Select all

MMC1-WRAM+CE--+--<|--+- RAM+CE
              |      |
              +--1k--+
              |      |  
             100k   56p 
              |      |  
             GND    GND 

mightydidz
Posts: 30
Joined: Wed Jan 24, 2018 12:04 pm

Re: AX5904 WRAM control

Post by mightydidz » Tue Oct 13, 2020 3:17 pm

mightydidz wrote:
I'm just concerned about this delay your mentioning compared to MMC1B2?
I'm not an expert with scope, but your comparing M2 and Wram+ce?
Correct me, but I dont see any Wram+ce on AX5904?
what about pin 6?
Sorry, I'm blind I was checking Kaiser Clone on wiki.
Since AX5904 is the same pinout as official MMC1, I'll use pin 6 with an 74'00 inverter.

mightydidz
Posts: 30
Joined: Wed Jan 24, 2018 12:04 pm

Re: AX5904 WRAM control

Post by mightydidz » Tue Oct 13, 2020 9:00 pm

I will use a 62256 wram. Do i need the same 56p rc delay on ram-!ce with the inverter?

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