Micropower |
Volume 1 · Number 2 · September 1981 |
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the NMI handling routine. Here bit 3 of port 0 is reset, and CONFLG is tested to see if the program has arrived at this point from an E command (in which case CONFLG is not zero), or from some other source, such as a single step command, a breakpoint, or a hardware NMI. If it came an E command CONFLG is now set to zero, so that a subsequent NMI is handled correctly, if a breakpoint has been entered Restart 32 (£E7) is inserted, and the NMI handling routine jumps back to the executed program with a RETN. At last the program you started with Exxxx is running. You will see what happens if CONFLG is zero when we discuss the single step command.
F is not a valid command letter in either Nas-Sys 1 or Nas-Sys 3, and an error message is produced when it is entered. I use the command for a Find routine, which searches from a specified address for a string of up to 9 bytes.
| 2B | FIND | DEC HL | HL holds start address |
| 3A 0B 0C | LD A, (ARGN) | Get number of values | |
| FE 02 | CP 2 | Must be at least 2 | |
| 30 03 | JR NC, VALID | If so, continue | |
| DF 6B | SCAL ERRM | iF not, print Error | |
| C9 | RET | and end routine | |
| 3D | VALID | DEC A | Get string length |
| 4F | LD C, A | Save string length in C | |
| 41 | SRCHLP | LD B, C | Transfer to B |
| 11 0E 0C | LD DE, £0C0E | Point DE to first byte | |
| 1A | LD A, (DE) | Get first byte | |
| 23 | SRCH1 | INC HL | Look for first byte |
| BE | CP (HL) | Found it? | |
| 20 FC | JR NZ, SRCH1 | If not, continue to look | |
| 05 | DEC B | Only on byte to find | |
| 28 09 | JR Z, CALLDS | If so, go to display | |
| 13 | SRCH2 | INC DE | If not, look for second |
| 13 | INC DE | Get next in string | |
| 1A | LD A, (DE) | Go to next memory byte | |
| 23 | INC HL | Are they the same? | |
| BE | CP (HL) | If not, start again | |
| 20 ED | JR NZ, SRCHLP | Look for rest of string | |
| 10 F7 | DJNZ SRCH2 | All found, so tabulate | |
| D7 08 | RCAL TAB | Wait for keypress | |
| CF | RST 8 | Is it an escape? | |
| FE 1B | CP "ESCAPE" | Look for next string | |
| 20 E4 | JR NZ, SRCHLP | Output, CR | |
| DF 6A | SCAL CRLF | End routine | |
| C9 | RET |
* * TAB routine starts here * *
The TAB routine used by the above program is the same as the one in the comparison routine, and the code for this should be entered at the position marked above. Of course, if you use both the compare and the Find routine,
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