Lpc2000

Hello all,

I am having an issue here and I hope someone has some suggestions.  I'm 
trying to interface some LCDs to my micro, I have a graphical 128x64 which 
has an embedded controller chip interfaced fine, using P1.16-P1.23 as 8-bit 
parallel IO.  However when I try to hook up a SED13305 the data seems to 
get corrupted.  I'll issue a write to the device to store something in 
VRAM, then immediately try to read it back.  Here's where things get weird.

If I try to use the WR and RD signals like they should be used (RD always 
high, Clear WR, Set Byte, Set WR), the write appears to work, however 
repeated reads of the same memory area return different results each 
time.  Enough reads show that the data was written successfully.  However 
if I modify only the write routine to use the WR and RD signals in a 
different (wrong) way (Clear WR, Set RD, Set Byte, Set WR, Clear RD) then 
repeated reads return the same data every time, however bits 7:8 are always 
"10".  Note that the read routine is the exact same both times.

How is it possible to have a small change to the write routine effect how 
the read routine works?

I have tried playing with timing to no avail.  I looked at everything with 
an oscilloscope and the timing and data look correct.  I've verified all 
connections with a multimeter. I have both the micro and the SED running 
off of 3.3V.  Note that if the SED is running at 5V then I get complete 
garbage on read (meaning probably nothing worked), even though the SED says 
it works from 2.7V to 5.5V.

I think I'm going to have to try to make another test board, but before I 
run out to do that does anyone have any ideas as to why this is happening?

Thanks,

-- Sean