Hi, I have a small issue with printing out the ASCII char set, from $20 to $7E inclusive. The 8251 initialisation is okay 'cos I ran a small program to print a single char to the TTY and it worked fine. So, I thought I'd expand on this to transmit the printable ASCII char set to the TTY (actually, Hyperterm). However, it jusat transmits spaces. I've tried a few variations and it never prints the chars properly. I'm figuring that there is a problem with my logic, but as I don't have a SC/MP programming manual and I can't see the forest due to the trees, I'm hoping someone here on this list with some SC/MP programming knowledge maybe able to offer some assistance. The P1 register is pointing to the 8251 data port, and 1(1) points it to the control/status port. ktest: ldi $20 ;First char is ASCII 'space' kt1: xae ;temp save in E-reg/exchange the A and E regs kt2: ld 1(1) ;get UART status ani $01 ;Tx Ready? jz kt2 ;No, keep checking lde ;Yes, get char st (1) ;Tx the char scl ;carry = 1 adi $00 ;add 0 + carry xae ;save to E reg lde ;move back to A reg xri $7f ;gone too far? jz ktest ;yes, start at SPACE again jmp kt1 ;no, print it Basically, I load the A reg with ASCII $20 (SPACE) and save it to the E reg. Then I check the 8251 TX Ready flag and when ready I get the ASCII char from the E reg and transmit it. The char is still in the A reg after the transmission, so I set the carry bit and add $00 (ie incrementing the A reg). I then save this value in the E reg and then load it back to the A reg - thereby both A and E regs have the same value. I then check if I have hit the end by destroying the A reg with the XRI instruction. If I haven't hit the end ($7F) yet, I go back to "kt1", whcih relaods the A reg with the char and then it goes on to print this char. If it's at the end then it goes back to "ktest" to start back at ASCII $20 and does it over again. I've done this heaps of time with the 8080 processors and don't know why it's not doing it with the SC/MP. Also, I have some SC/MP listings about and one of them has "LD @0(P2)" instruction. decrement bit and you must specify the displacement for the inc/dec. If this is the case, then what does the "0" that immediately follows the "@" do? I would expect to see a value other than "0" to ensure the P2 register is inc/dec by the appropriate amount. Please, old SC/MP dudes, any help would be greatly appreciated. river