Thanks for that Rob, this will be of great help to me. I am using the following asynchronous sequence to read a byte from the RPC to the host
1. SP2 will assert RX Request line low to initiate transfer
2. Host pulls TX Accept low (i.e. request is accepted by host)
3. SP2 will turn on its bus drivers, place LS nibble onto data lines.
4. Negate RX Request (set to 1)
5. Host reads the data and negates RX accept( i.e data has been accepted).

I have come up with the following code to carry out the sequence

CLR RXR
WAITRQ JNB RXA,WAITRQ

SETB RXR
WAITRQ1 JBC RXA,WAITRQ1

Am i goin about this sequence the right way and could you help me out with this and how i may be able to implement this for sending AAhex.
Declan