Hello,

First off I want to thank all of your for your help over these last few months. I couldn't have done it without your help! Happy 4th!

Now for the question, which is a little in depth for me,

I'm building a robot using a 8051 system that I've been working on. I've decided on using one of my 8-bit ports as a 4bit address, 4 bit data bus system for output motor control only. Using a 74HC135 demultiplexor for address decoding, and 74HC373s for latching I will be able to control up to 15 motors with 16 speeds (including stop) each.

For example, to make the robot go full speed (assuming the adressing for the left motor was on an 0001, and the right motor was on 0010), a simple MOV P2, #0001111b and MOV P2, #0010111b would make the robot go foreward full speed.

My problem is that I'm still struggling with registers and memory on the 8051 in ASM. Could anybody show me or write a small ASM program that could count from 0-15 in binary and writing it to port 2, while keeping the first four bits the same?

So the output on P2 would, for example be :
00100001
00100010
00100011
00100100
00100101
00100110
00100111
etc up to
00101111
and then loop back to
00100001 and repeat.