help me communicate with 8255!

[vanbayhoang]

Please can any one provide me asemble code for communicate with 8255 using at89c51!
thanks!

 

[IanP]

Here is a good starting point:
**broken link removed**

Rgds,
IanP

 

[vanbayhoang]

thanks!
you have asembly code? I need code asembly!
sorry!, My english is not good.

 

[IanP]

First, map 8255 as an external memory - that's the easiest way ..
See attached picture ..
On power on all mode/direction bits in the Control Register are set to "0" and that means that all 3 ports are set to be outputs ..

To send data to, say, port A, use the following command:

MOV DPTR, #addres of A; in this example it is #4000h
MOV A, #what you want to send
MOVX @DPTR, A

Other addresses are as follows:
Address 4000H: port A
Address 4001H: port B
Address 4002H: port C
Address 4003H: configuration register

To set Port A as inputs, you have to set D4 in the Control Register.

MOV DPTR, #4003h
MOV A, #00010000b
MOVX @DPTR, A

and then:

MOV DPTR, #4000h; addres of Port A
MOV A, @DPTR

will read PORT A of the 8255 ..

Rgds,
IanP

 

[vanbayhoang]

thanks for your help!
have fun!