$FFD2 is address of the Commodore 64 kernal routine to print a character. From the Commodore 64 Programmer's Reference Guide: B-5. Function Name: CHROUT Purpose: Output a character Call address: $FFD2 (hex) 65490 (decimal) Communication registers: A Preparatory routines: (CHKOUT,OPEN) Error returns: 0 (See READST) Stack requirements: 8+ Registers affected: A Description: This routine outputs a character to an already opened channel. Use the KERNAL OPEN and CHKOUT routines to set up the output channel before calling this routine, If this call is omitted, data is sent to the default output device (number 3, the screen). The data byte to be output is loaded into the accumulator, and this routine is called. The data is then sent to the specified output device. The channel is left open after the call. +-----------------------------------------------------------------------+ | NOTE: Care must be taken when using this routine to send data to a | | specific serial device since data will be sent to all open output | | channels on the bus. Unless this is desired, all open output channels | | on the serial bus other than the intended destination channel must be | | closed by a call to the KERNAL CLRCHN routine. | +-----------------------------------------------------------------------+ How to Use: 0) Use the CHKOUT KERNAL routine if needed, (see description above). 1) Load the data to be output into the accumulator. 2) Call this routine. EXAMPLE: ;DUPLICATE THE BASIC INSTRUCTION CMD 4,"A"; LDX #4 ;LOGICAL FILE #4 JSR CHKOUT ;OPEN CHANNEL OUT LDA #'A JSR CHROUT ;SEND CHARACTER