Honda ECU Air Conditioning Control Routine Analysis
Technical breakdown and assembly commentary for the Honda ECU air conditioning control routine.
This document provides a technical breakdown of the air conditioning (A/C) control routine found within the Honda ECU firmware. The following assembly code analysis explains the logic gates and memory offsets used to manage the A/C clutch output.
A/C Routine Assembly Breakdown
| Address | Opcode | Instruction | Description |
|---|---|---|---|
| 4306 | DA 11 17 | JBR off 11.2 | Jump if bit 2 of offset 11 is set (A/C switch input) |
| 4309 | C4 26 1C | SB off 26.4 | Set bit 4 of offset 26 to 1 |
| 430C | F4 E2 | LB A, off E2 | Load offset E2 to lower byte of accumulator |
| 430E | CE 1B | JNE 432B | Jump to 432B if not equal |
| 4310 | C4 E3 98 32 | MOVB off E3, #32 | Move value #32 to offset E3 |
| 4314 | C4 1B 18 | SB off 1B.0 | Set bit 0 of offset 1B to 1 |
| 4317 | 95 | RC | Reset carry (C = 0) |
| 4318 | CB 15 | SJ 432F | Short jump to 432F |
| 431A | C4 B8 15 | CLRB off B8 | Clear all bits of offset B8 |
| 431D | C4 E3 15 | CLRB off E3 | Clear all bits of offset E3 |
| 4320 | C4 26 0C | RB off 26.4 | Reset bit 4 of offset 26 |
| 4323 | F4 E3 | LB A, off E3 | Load value of offset E3 to accumulator |
| 4325 | CE ED | JNE 4314 | Jump to 4314 if not equal |
| 4327 | C4 E2 98 32 | MOVB off E2, #32 | Move value #32 to offset E2 |
| 432B | C4 1B 08 | RB off 1B.0 | Reset bit 0 of offset 1B |
| 432E | 85 | SC | Set carry (C = 1) |
| 432F | C5 20 38 | MB 20.0, C | A/C Clutch output control |
Note
The routine utilizes specific memory offsets to track the state of the A/C request and the subsequent clutch engagement. Ensure that any modifications to these offsets account for the timing requirements of the A/C compressor clutch relay.
Important
The instruction at address 432F (
MB 20.0, C) is the final output stage for the A/C clutch. Modifications to the preceding logic will directly impact the duty cycle or engagement state of the compressor.