This thread has been very helpful but the PBP manusl seems misleading:

1. It would only take a line to explain that the Control byte always starts 1010.

2. In the examples, the Control byte for the smaller chips is given as %1010xxx0 and x means 'don't care.' It does matter is your chip has a hard wired address. e.g

A2 to G, A1 to G, A0 to VCC - xxx becomes 001.
A2 to VCC, A1 to G, A0 to G - xxx becomes 100 etc.

3. Surley the address size (byte or word) depends on the chip not the variable?

It took me 2.5 days to arrive at my present 'thin' understanding - this seems par for the course with this command. If I still have some of the above wrong - please reply.

Bill Legge