RE: C128 'VIC tower' mod board

From: Jeffrey Birt <*birt_j_at_soigeneris.com*> Date: Sun, 19 Jul 2020 13:43:17 -0500 Message-ID: <025001d65dfc$7804f1a0$680ed4e0$_at_soigeneris.com> · birt_j_at_soigeneris.com

I have looked at th(RHrd), tsu(WRH) and tCLRH and they all seem fine with either /RAS for read or writes. It is rather curious. Maybe there is some odd edge case where you need to know exactly where and when to look to see the problem. 

I also swapped in the R4 VIC2 into my C128 which does not have the mod board and it worked fine. So, it is back to possibly being about the slower RAM?

If anyone is so inclined you can download the Saleae Logic software for free and look at the data too: https://www.saleae.com/downloads/ 

Jeff Birt

-----Original Message-----
From: Gerrit Heitsch <gerrit_at_laosinh.s.bawue.de> 
Sent: Sunday, July 19, 2020 10:53 AM
To: cbm-hackers_at_musoftware.de
Subject: Re: C128 'VIC tower' mod board

On 7/19/20 5:21 PM, Jeffrey Birt wrote:
> /RAS has a low time of 292ns
> /RAS_FF has a low time of 375ns
> 
> It seems that /RAS has a sufficient dwell time so it must be more subtle than that. I have looked at things like TRLCH and TCLRH and they look to be within spec with either version of /RAS. I am sure there is something subtle I am missing.

When /RAS goes HIGH, the RAM goes offline and vanishes from the bus. 
Maybe that's too early, especially on a write cycle?

  Gerrit