Hi there! I know that this subject is old and it has been discussed several times. I tried searching in the forums, but could not find something useful.

Here is my problem. I am interfacing PC AT keyboard to 89C51. There are certain commands that you send to the keyboard, like 0xFF (reset) and 0xED (set status LEDs) etc etc.

Of all the website that I have visited, all of them say that the keyboard DOES NOT reply with an acknowledgement if a RESET COMMAND is sent to it. However, in my case, I AM getting an acknowledgement.

Here is what happens. I get the data from PC keyboard and send it to PC via serial port. Likewise, I get commands from PC serial port and send them to the keyboard. "KEYBOARD CLOCK" is tied to INT0 of microcontroller.

P.S. I inhibit the transmission by pulling the "KEYBOARD CLOCK" line low, so I can transmit the keyboard received byte to the PC.

Following is the dump I get on the PC, when I send it the RESET command..

-------------------------------------
0xFF (command sent to keyboard)

0x00 (ack bit - last bit in the command byte)
0xFA (ack from keyboard)
0xAA (BAT success)
-------------------------------------

Can the PC keyboard toggle all 3 LEDs (CAPS,SCROLL,NUM) togather ?? Because when I send it the command to change LED status, this is what happens (I have hardcoded in uC to send 0x7 - set all LEDs - immediately after SET LED COMMAND)

-------------------------------------
0xED (command sent to keyboard)
0x00 (ack bit - last bit in the command byte)
0xFA (ack from keyboard)

0x07 (argument byte sent to keyboard)
0x00 (ack bit - last bit in the command byte)
0xFE (re-transmit last byte)
-------------------------------------


The PC, I guess, never sends it command to toggle all LEDs togather (since each key has a separate scan code). Could it be that there is a check that only one bit be set in the 3 least significant bits ??

H E L P ! ! !

Regards
Aman