The commands depend on the LCD. Basically what you are going to want to do is set up the command register first and then load the data register. For example if PortA was at 0x392 then you could do this
This is assuming that 91H sets all the command register for say 2x20 line lcd screen, set's the curser to blink and set it at the beginning of the first line.
mov dx, 392H
mov ax, 91H
out dx, ax
Then say your data register was at 393H. You could send data out the same way. So put that in an _ASM directive and use an unsigned char to hold the ascii text [You said 8-bit interface] to transfer the data.
Other than that could you give the model number of the lcd?