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Add Registers

zxq5
2025-06-19 17:38:12 +01:00
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Registers.md
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## Registers
Below is a list of the registers:
| Hex | Register | Description |
|----------------|----------|-----------------------------------------------------------------------------|
| System | MAR | Memory address register for the current instruction to be fetched from RAM.|
| System | STS | Status register, stores flags from calculations and comparisons. |
| System | CIR | Current instruction register. |
| System | PCX | Program counter. Stores the address of the next instruction |
| 0x00\dots 0x07 | RG0 \dots RG7 | General purpose registers for variables etc. |
| 0x08 | ACC | Accumulator for storing outputs of calculations. |
| 0x09 | MDR | Memory data register for moving data between RAM and registers |
| 0x0A | SPR | Stack pointer. |
| 0x0B | BPR | Stack base pointer. |
| 0x1C | RET | Return address register. |
| 0x1D | IDR | Interrupt descriptor register. Contains a pointer to the interrupt descriptor table.|
| 0x11\dots 0x1F | RESERVED | Reserved registers.
## STS --- Status Register
The status register stores the flags from calculations and comparisons. It is a register of 32 bits, with the following layout:
| Bit | Name | Description | Boot Value |
|--------|--------------------|-----------------------------------------------------------------------------------------------|------------|
| 0 | Equal | Set if the result of the last comparison was equal. | 0 |
| 1 | GreaterThan | Set if the result of the last comparison was greater than. | 0 |
| 2 | GreaterThanOrEqual | Set if the result of the last comparison was greater than or equal. | 0 |
| 3 | LessThan | Set if the result of the last comparison was less than. | 0 |
| 4 | LessThanOrEqual | Set if the result of the last comparison was less than or equal. | 0 |
| 5 | Zero | Set if the result of the last arithmetic / logic operation was equal to zero | 0 |