Re: external memory problem

Not that I know the RAM, but it seems as if you might mix a TTL level 
device (both 74F573 and 74HCT573) with a CMOS device (IS62C1024-35)
Look at the requirements for a HI input of the RAM and see if the TTL 
device will garantee that high voltage.
Your logic probe does _not_ measure the exact voltage !
If that is causing the problem, you can "help" the TTL device by adding 
pull-up resistors in the output of the TTL (input CMOS device)
That my idea
Cheers

Ed skrev:
> I am using a 89C450MCL mcu running at 29.492mhz
> With just the micro, 74F573 (or 74HCT573 tried both) and a IS62C1024-35
RAM 
> chip it seems I loose the address sometimes at the output of the latch
when 
> /WR goes low.
> I am using plenty of bypas caps and 4.6uf caps for supply lines.
> I am simply trying to clear a memory range from 0000h - 00FFh.
> I put my logic probe on the address lines of the RAM chip after the
latch 
> and I can see the address sometimes going wrong.
> See http://www.eddie1.net/timing.jpg
for reference.
> As you can see I am just writing to memory and as the image shows 1Ch is

> fine 1Dh is fine but 1Eh and 1Fh are dropping the address then 20h is
fine 
> and 21h is fine.
> This is not the only place it goes wrong and I cannot find any
corelation in 
> the locations that go wrong.
> Any ideas??
> 
>