BASIC IV ROM Routines
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Submitted by Steve Fewell
Routine: bcopya
Name: Copy FWA to FWB
Starting Address: &A40B
Entry criteria: None
Exit: Copies the value of the FWA to the FWB.
Description:
Sets every byte of the FWB to a copy to the corresponding FWA byte as follows:
Byte Description |
FWA |
FWB |
| Sign | &2E ---> | &3B |
| Overflow | &2F ---> | XX Not copied |
| Exponent | &30 ---> | &3C |
| Mantissa 1 | &31 ---> | &3D |
| Mantissa 2 | &32 ---> | &3E |
| Mantissa 3 | &33 ---> | &3F |
| Mantissa 4 | &34 ---> | &40 |
| Mantissa 5 / Rounding | &35 ---> | &41 |
The FWB now holds the same value as the FWA.
Disassembly for the Copy FWA to FWB routine
| A40B | . | 165 046 | A5 2E | LDA &2E |
| A40D | ; | 133 059 | 85 3B | STA &3B |
| A40F | 0 | 165 048 | A5 30 | LDA &30 |
| A411 | < | 133 060 | 85 3C | STA &3C |
| A413 | 1 | 165 049 | A5 31 | LDA &31 |
| A415 | = | 133 061 | 85 3D | STA &3D |
| A417 | 2 | 165 050 | A5 32 | LDA &32 |
| A419 | > | 133 062 | 85 3E | STA &3E |
| A41B | 3 | 165 051 | A5 33 | LDA &33 |
| A41D | ? | 133 063 | 85 3F | STA &3F |
| A41F | 4 | 165 052 | A5 34 | LDA &34 |
| A421 | @ | 133 064 | 85 40 | STA &40 |
| A423 | 5 | 165 053 | A5 35 | LDA &35 |
| A425 | A | 133 065 | 85 41 | STA &41 |
| A427 | ` | 096 | 60 | RTS |
