Semiconductor & Computer Engineering
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μCOM-4 ISA - NEC
The μCOM-4 ISA was an instruction set architecture composed of 80 instructions that were implemented by the NEC in their μCOM-4 family of microcontrollers. The μCOM-43 family implemented the complete ISA, while the μCOM-44 and μCOM-45 families implemented a strict subset of it. (Note that the μCOM-42 family had its own instruction set.)
Block diagram
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Registers
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Features
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Instructions
The μCOM-43 has support for all 80 instructions. The μCOM-44/μCOM-45 support a strict subset of it composed of 58 instruction. The majority of those 22 instructions deal with the added features only found in the μCOM-43 models.
| Mnemonic | OPCode | Bytes | Cycles | Function | Meaning | Skip Condition |
|---|---|---|---|---|---|---|
| CLA | 90 | 1 | 1 | ACC ← 0 | Clear accumulator | |
| CMA | 10 | 1 | 1 | ACC ← ~ACC | 1-s complement accumulator | |
| CIA | 11 | 1 | 1 | ACC ← ~ACC + 1 | 2-s complement accumulator | |
| INC | 0D | 1 | 1 + skip | ACC ← ACC + 1 | Increment accumulator, skip if overflow | on overflow |
| DEC | 0F | 1 | 1 + skip | ACC ← ACC - 1 | Decrement accumulator, skip if underflow | on underflow |
| CLC | 0B | 1 | 1 | C ← 0 | Clear carry flag | |
| STC | 1B | 1 | 1 | C ← 1 | Set carry flag | |
| XC | 1A | 1 | 1 | C ↔ C' | Exchange carry flag with carry save | |
| RAR | 30 | 1 | 1 | C → ACC → C | Rotate accumulator right through carry flag | |
| INM | 1D | 1 | 1 + skip | (DP) = (DP) + 1 | Increment RAM content pointed by DP, skip if result is zero | on (DP) = 0 |
| DEM | 1F | 1 | 1 + skip | (DP) = (DP) - 1 | Decrement RAM content pointed by DP, skip if result is 0Fh | on (DP) = 0Fh |
| AD | 08 | 1 | 1 + skip | ACC ← ACC + (DP) | Add RAM content pointed by DP to accumulator, skip if overflow | on overflow |
| ADS | 09 | 1 | 1 + skip | ACC ← ACC + (DP) + C; C ← 1 on overflow | Add RAM content pointed by DP with carry to accumulator, if overflow set carry flag and skip | on overflow |
| ADC | 19 | 1 | 1 | ACC ← ACC + (DP) + C; C ← 1 on overflow | Add RAM content pointed by DP with carry to accumulator, if overflow set carry flag | |
| DAA | 06 | 1 | 1 | ACC ← ACC + 6 | Decimal adjust accumulator for BCD addition | |
| DAS | 0A | 1 | 1 | ACC ← ACC + 10 | Decimal adjust accumulator for BCD subtraction | |
| EXL | 18 | 1 | 1 | ACC ← ACC ^ (DP) | Exclusive-or accumulator with RAM content pointed by DP | |
| LI | 1 | |||||
| S | 1 | |||||
| L | 1 | |||||
| LM | 1 | |||||
| X | 1 | |||||
| XM | 1 | |||||
| XD | 1 | |||||
| XMD | 1 | |||||
| XI | 1 | |||||
| XMI | 1 | |||||
| LDI | 2 | |||||
| LDZ | 1 | |||||
| DED | 1 | |||||
| IND | 1 | |||||
| TAL | 1 | |||||
| TLA | 1 | |||||
| XHX | 1 | |||||
| XLY | 1 | |||||
| THX | 1 | |||||
| TLY | 1 | |||||
| XAZ | 1 | |||||
| XAW | 1 | |||||
| TAZ | 1 | |||||
| TAW | 1 | |||||
| XHR | 1 | |||||
| XLS | 1 | |||||
| SMB | 1 | |||||
| RMB | 1 | |||||
| TMB | 1 | |||||
| TAB | 1 | |||||
| CMB | 1 | |||||
| SFB | 1 | |||||
| RFB | 1 | |||||
| FBT | 1 | |||||
| FBF | 1 | |||||
| CM | 1 | |||||
| CI | 2 | |||||
| CLI | 2 | |||||
| TC | 1 | |||||
| TIT | 1 | |||||
| JCP | 1 | |||||
| JMP | 2 | |||||
| JPA | 1 | |||||
| EI | 1 | |||||
| DI | 1 | |||||
| CZP | 1 | |||||
| CAL | 2 | |||||
| RT | 1 | |||||
| RTS | 1 | |||||
| STM | 2 | |||||
| TTM | 1 | |||||
| SEB | 1 | |||||
| REB | 1 | |||||
| SPB | 1 | |||||
| RPB | 1 | |||||
| TPA | 1 | |||||
| TPB | 1 | |||||
| OE | 1 | |||||
| OP | 1 | |||||
| OCD | 2 | 2 | PORT[C,D] ← I7-I0 | |||
| IA | 2 | 2 | ACC ← PORT[A] | |||
| IP | 1 | 1 | ACC ← PORT[DPL] | |||
| NOP | 1 | 1 | no operation |
- μCOM-43 only
Documents
References
- NEC Electronics (Europe) GmbH, 1982 Catalog, "μCOM-4: 4-Bit Single Chip Microcomputer Family", 143-176 pp.