AVR-Chat

I am having trouble understanding how a character is sent to the lcd 
display by way of at-keybd. I am using stk500 with 8515 mcu and 4x20 
lcd. I am using portd-pd2(int0) for clock and pd5(oc1a) for data. My 
question is,do I need a pysical connection from 8515 to lcd in order 
to pass data to lcd or is this passed by way of software code. My lcd 
is wired using porta and is currently working. I just want to grasp
an 
understand of the flow of data from keybd to lcd. Is the uarts 
transmit data out pin pd1 used(hardwired) or is it just coded via 
software to send data stored in registers and transmitted out to lcd. 
Is this what is meant by (softuart) or am I missing something here. 
Any help would be appreciated.