The BBC and Master Computer Public Domain Library
BC51 Push String to Stack
Submitted by Steve Fewell
Description:
Check whether there is space for the length of the String in the String Buffer (SWA) plus 1 byte (for length)
on the stack. If no space, then generate "No Room" error.
Y = length of the String Buffer (?&36, Length of SWA). If length is zero then store
binary zero on the Stack (length of String) and return, as the first byte retrieved from
the Stack will be the String length, 0 in this case.
Otherwise, store the String on the Stack (in reverse order).
Lastly, the length of the string is stored on the stack (?&36) [last byte of Stack Value] and routine exits.
Disassembly for the Push String to Stack routine
| BC51 | 024 | 18 | CLC | |
| BC52 | 165 004 | A5 04 | LDA &04 | |
| BC54 | 6 | 229 054 | E5 36 | SBC &36 |
| BC56 | 032 030 189 | 20 1E BD | JSR &BD1E Check for Stack clash with Heap | |
| BC59 | 6 | 164 054 | A4 36 | LDY &36 |
| BC5B | 240 008 | F0 08 | BEQ 8 --> &BC65 | |
| BC5D | 185 255 005 | B9 FF 05 | LDA &05FF,Y | |
| BC60 | 145 004 | 91 04 | STA (&04),Y | |
| BC62 | 136 | 88 | DEY | |
| BC63 | 208 248 | D0 F8 | BNE -8 --> &BC5D | |
| BC65 | 6 | 165 054 | A5 36 | LDA &36 |
| BC67 | 146 004 | 92 04 | STA (&04) | |
| BC69 | ` | 096 | 60 | RTS |
