Lpc2000

Sean,

I have used the SED 1335 in the past.  One thing that is too
obvious is that the SED part is probably not the fastest thing
in the world, and you may be exceeding it speed capability.

I never had this problem with the Z80 family I was using at the
time, but the new ARM chips are way too fast for the 1335, I do not
know about the chip you are using.

Just a thought.

Glen


Sean wrote:

> 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
> 
> 
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> Yahoo! Groups Links
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