Daren sez:

... snip snip ...

> The software/hardware works fine with a 16C55, but when I recompiled to
> a 16C71, using the same circuit/clock speed etc the LCD won't respond.
> I have adjusted the source code to take care of the different start address
> and interupts etc in the '71.
>
> I know the '71 works, as I have tested it by pulsing port a&b and watching
> the pins with a logic probe.
>
> My first thought was timing, so I slowed the '71 down by adjusting the
> delay loops but it still doesn't work.

... snip snip ...

The problem could lie in the initialization of the LCD. Hitachi only
guarantees 'Initializing by internal reset circuit' if the rise time of the
power supply to the LCD is within 0.1ms to 10ms. Furthermore, they say "if
the lower width of power OFF (less than .2V) is less than 1ms, the internal
reset circuit will not operate normally...". In such case, 'Initializing by
Instruction' is to be done. The procedure is somewhat longish to be
described here, but source code (Parallax asm for '84) is available from me
upon request. Another strange thing about the LCDs using the Hitachi HD44780
controller is that they don't like noisy PSU rise times (they lock and get
red hot). It is therefore recommended to power them up using one of the port
pins.

Hope this helps, Darren.

Regards

Richard Ivanov  divanov@plessey.co.za