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BBC Micro Elite

Text: cpl

Name: cpl [View in context] Type: Subroutine Category: Text Summary: Print the selected system name
Print control code 3 (the selected system name, i.e. the one in the crosshairs in the Short-range Chart). Other entry points: cmn-1 Contains an RTS
.cpl { LDX #5 \ First we need to backup the seeds in QQ15, so set up \ a counter in X to cover three 16-bit seeds (i.e. \ 6 bytes) .TT53 LDA QQ15,X \ Copy byte X from QQ15 to QQ19 STA QQ19,X DEX \ Decrement the loop counter BPL TT53 \ Loop back for the next byte to backup LDY #3 \ Step 1: Now that the seeds are backed up, we can \ start the name-generation process. We will either \ need to loop three or four times, so for now set \ up a counter in Y to loop four times BIT QQ15 \ Check bit 6 of w0_lo, which is stored in QQ15 BVS P%+3 \ If bit 6 is set then skip over the next instruction DEY \ Bit 6 is clear, so we only want to loop three times, \ so decrement the loop counter in Y STY T \ Store the loop counter in T .TT55 LDA QQ15+5 \ Step 2: Load w2_hi, which is stored in QQ15+5, and AND #%00011111 \ extract bits 0-4 by AND'ing with %11111 BEQ P%+7 \ If all those bits are zero, then skip the following \ 2 instructions to go to step 3 ORA #%10000000 \ We now have a number in the range 1-31, which we can \ easily convert into a two-letter token, but first we \ need to add 128 (or set bit 7) to get a range of \ 129-159 JSR TT27 \ Print the two-letter token in A JSR TT54 \ Step 3: twist the seeds in QQ15 DEC T \ Decrement the loop counter BPL TT55 \ Loop back for the next two letters LDX #5 \ We have printed the system name, so we can now \ restore the seeds we backed up earlier. Set up a \ counter in X to cover three 16-bit seeds (i.e. 6 \ bytes) .TT56 LDA QQ19,X \ Copy byte X from QQ19 to QQ15 STA QQ15,X DEX \ Decrement the loop counter BPL TT56 \ Loop back for the next byte to restore RTS \ Once all the seeds are restored, return from the \ subroutine }