Re: 89C51ED2

On Sep 4, 8:58 pm, "TT_Man" <Some...@xxxxxxxxxxxx> wrote:
How does the defect manifest itself ?

8051s have been 'rock solid' IME. As someone else memtioned, do you have a
critical timing issue anywhere ? Like an I/F chip maybe ? Are PSEN, ALE,
/WR
and /RD all clean ? You're probably not using PSEN but never hurts to
check.

No-one's messed about with the clock oscillator parts have they ?

What do the 10 lines of code do ?

Graham

An extra speech phrase is output.... ALE PSEN /wr/rd are all unused as the
device is a 64K flash part. We have several generations of board that all
support various chip types, 52, 53 ED2 etc. The faulty ED2's will not
execute correctly in any board.
The 10 lines of code basically index a speech phrase and output it 3 times
to a dac. Then the routine checks an input and proceeds or not via a branch.
somewhere in these lines of code, another speech phrase is output. Speech is
terminated via a null byte. The extra speech phrase in not contiguous with
the correct phrases, so it's not going to be a DPHL corruption...that
somehow skips the null byte detection.

Does the code have interrupts enabled?

Is it written in ASM or C?

What does the code do right as it comes out of reset? Would it
perhaps play this phrase?

What is the clock speed and what does the VCC look like?

.