Background:

I have tried using two different compilers to drive this display (Toshiba
TLX-1741-C3M).  I can write to the display fine, but cannot read anything
from it.  I'm using an 89s53 (8052 type) CPU.  This CPU is strange in that
the I/O ports don't use direction bits to control them.  To read the port
you write 0xFF to the port, and then read it.  The ports are open collector
with internal pull-ups.  This allows an external device to drive the pins
low (over-riding the internal pull-ups).  According to the datasheet it is
pretty much impossible for and external device to drive the pins high
(over-riding the 0 outputting from the pin)  At first when trying to read
the display, I was unaware of the way the 8052 ports work (newbie to 8052).
Therefore, some of the bits (in the port) were set to 0 when I commanded the
LCD to give me the status.  ;-(

Question:

Is it possible that the 8052 "sunk" enough current (due to 0's in the port)
to damage (burn out) the outputs of the LCD display?  It does not appear
that the 89s53 is damaged in any way (I tested the port using a keypad
scanning routine, and all is well).  There is no way that I can get the
display to cough up it's status and hold it, while I disconnect the display
from the CPU to see if it's outputs are working.

Thanks for any help or advice.

Michael Brown
Instant Net Solutions
www.KillerPCs.net

"In the land of the blind, he who has one eye is king"

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