| Jump back if we've got a space char, since we're not interested in spaces. | ||||
| 045E | FE20 | NextChar_tail | CPI ' ' | |
| 0460 | CA1000 | JZ NextChar | ||
| Set carry flag if char >= '0'. | ||||
| 0463 | FE30 | CPI '0' | ||
| 0465 | 3F | CMC | ||
| Test for null char without affecting carry flag. | ||||
| 0466 | 3C | INR A | ||
| 0467 | 3D | DCR A | ||
| 0468 | C9 | RET | ||
Resets the data pointer to just before the start of the program.
| 0469 | EB | Restore | XCHG | |
| 046A | 2A6501 | LHLD PROGRAM_BASE | ||
| 046D | 2B | DCX H | ||
| 046E | 226D01 | SHLD DATA_PROG_PTR | ||
| 0471 | EB | XCHG | ||
| 0472 | C9 | RET |
Apparently the Altair had a 'break' key, to break program execution. This little function tests to see if the terminal input device is ready, and returns if it isn't. If it is ready (ie user has pressed a key) then it reads the char from the device, compares it to the code for the break key (0x03) and jumps to Stop. Since the first instruction at Stop is RNZ, this will return at once if the user pressed some other key.
| 0473 | DB00 | TestBreakKey | IN 00 | Exit if no key pressed. |
| 0475 | E601 | ANI 01 | ||
| 0477 | C0 | RNZ | ||
| 0478 | CD8203 | CALL InputChar | ||
| 047B | FE03 | CPI 03 | Break key? | |
| 047D | C3F701 | JMP Stop |
If character pointed to by HL is alphabetic, the carry flag is reset otherwise set.
| 0480 | 7E | CharIsAlpha | MOV A,M | |
| 0481 | FE41 | CPI 'A' | ||
| 0483 | D8 | RC | ||
| 0484 | FE5B | CPI 'Z'+1 | ||
| 0486 | 3F | CMC | ||
| 0487 | C9 | RET |
Gets the subscript of an array variable encountered in an expression or a DIM declaration. The subscript is returned as a positive integer in CDE.
| 0488 | D7 | GetSubscript | RST NextChar | |
| 0489 | CD8A06 | CALL EvalExpression | ||
| If subscript is negative then jump to FC error below. | ||||
| 048C | EF | RST FTestSign | ||
| 048D | FA9804 | JM FunctionCallError | ||
| Likewise, if subscript is >32767 then fall into FC error, otherwise exit to FAsInteger. | ||||
| 0490 | 3A7201 | LDA FACCUM+3 | ||
| 0493 | FE90 | CPI 90 | ||
| 0495 | DA770A | JC FAsInteger | ||
| Invalid function call (FC) error.. | ||||
| 0498 | 1E08 | FunctionCallError | MVI E,08 | |
| 049A | C3D501 | JMP Error | ||