I'm not too sure why they suggest NANDing the upper address lines with ALE. As I mentioned before, you have two choices with interfacing this device:

a) As a bus device as per the datasheet. If it is the only device on the bus, I think it is ok just to connect the /cs pin to 0v. Assuming you connect the RS signal to A8 of the 8051 you would access the device as follows:

mov dptr,#0
movx a,@dptr ;read receive data reg

movx @dptr,a ;write transmit data reg

mov dptr,#8
movx a,@dptr ;read status reg

movx @dptr,a ;write control reg

The proviso here is that the micro you are using is <=16Mhz and a twelve clock part. Anything else and you may or may not be able to interface this way. The datasheet says read timing is 250nS - less than this and you'll have problems.


b) As a port pin driven device. This method you can use any of the port pins to drive the various signals. Assuming the 4 data bits are on P0..3 (you will most likely need pullup resistors on port0) and RS,READ,WRITE are the port pins connected for these functions to the mt8888c:

; read the receive data reg
mov P0,#$ff ;port pins to receive
clr RS
clr READ
mov a,P0
and a,#$0f ;low nibble only
setb READ

; write the transmit data reg
mov P0,a ;output the write data
clr RS
clr WRITE
nop
setb WRITE

similarly for the other registers you would setb RS with the above code.

Hopefully this clarifies the situation for you. Again, if you tell us what micro you are using we can give you more specific advice.