Thanks a lot, Andy, for your very detailed answer!
On Tue, 2 Jun 1998, Andy Kunz wrote:

>> (Topic: I bought 128K x 8 external program memory chips.)

> PROBLEM - You want 64K x 16.  The x8 won't fly!!
> ...
I meant: I bought 2 memory chips of 128K x 8 and use them in parallel.
(I don't use the upper 64K memory of the 128K. I had to buy these ones
because they are the cheapest with an access time of 45ns - suitable for
33 MHz clock frequency).
I found the general connection of external parallel memory in the
datasheets of the PIC17C75X. There is a (74HC)138 shown as the address
decoder, but not explained.

My idea is that I connect the 16 address lines of both memory chips in
parallel to the 74373s. The 2 x 8bit data lines are - of cause -
formed together to a 16 bit bus.
In my case it is different to yours: I don't need all possible external
memory, but only about 8K.
Is there any mistake in my idea?

> ...
> The GAL is totally optional.  You could just as well connect ALL the '373
> outputs directly to the memory chip.  Then you could run in microprocessor
> mode using a pre-programmed EPROM/FLASH/SRAM with no problem.
> ...

Can I run or do I HAVE TO run the PIC in microprocessor mode then ? Your
idea of a setup program in the internal memory is good. Lets presume this
for the question. Or: What happens when I use the external memory without
GAL and I use additionaly internal memory ?

> ...
> My method was developed to permit me to have a BIOS in the chip. (...)
> The BIOS supports the programming of the external RAM using a simple
> program.
> ...

Can I have a look on the bios code to have a hint for my application ?
(in case of copyrights - better send it directly to me:
A.Dante@City.ac.uk)

Thanks for the answers to the other topics that are now clear for me!

Andreas Dante