Mehdi,

I think it is as simple as:
- connect the data line directly to P0
- connect RD/WR to corresponding pins on '51 (P3.7/P3.6)
- connect HI/LO to any spare pin
- connect ACK to any other spare pin (e.g. int0 - maybe comes handy later)

Then the procedure to set a command would be
- set HI/LO to 0
- write low byte of the command using MOVX to any address
- set HI/LO to 1
- write high byte of the command using MOVX to any address

There is no address nor data register, just a single 16-bit register, and you have described nicely the 16-bit commands to be written to it, see chapter COMMAND SET page 37 on.

Then wait for ACK and read out the response 16-bit register, again low first.

That's all what I can see in the datasheet, and I don't think there will be more then this.

Good luck!

Jan Waclawek