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Various bug fixes to assembler, added more data pointers.

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Anachronaut
2026-08-13 23:41:22 -04:00
parent b50210d127
commit c2440ae5fa
38 changed files with 1028 additions and 236 deletions
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SplitBit Programming Manual.md
+16 -17
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@@ -3,7 +3,7 @@
SplitBit is a small 8 bit CPU.
It is a Harvard Architecture machine with a separate 64k memory space for its Program and another for its Data.
It has seven registers:
It has ten registers:
- The A and B Registers are each a general purpose 8 bit register.
- A and B are the operand registers for the ALU.
@@ -19,14 +19,13 @@ It has seven registers:
- The PC points to the current operation the CPU is executing, it initializes at Program Address 0x0000.
- The PC is only modified by the branch instructions and the CALL and RET instructions. It cannot be directly set by the programmer.**
- The Data Pointer is a 16 bit pointer into the Data Memory.
- The DP points to the current byte of data that the CPU can read or write to, it initializes at Data Address 0x0000.
- The DP can be set arbitrarily by the programmer to any value.
- The Data Pointers (0-3) are 16 bit pointers into the Data Memory.
- A DP points to the current bytes of data that the CPU can read or write to, it initializes at Data Address 0x0000.
- A DP can be set arbitrarily by the programmer to any value.
- The Stack Pointer is a 16 bit pointer into the Data Memory.
- The SP points to the current element of the stack, it initializes at location 0xFFFF.
- The SP value is only modified by the push and pop instructions and cannot be set by the programmer.
- The SP must always be greater than the DP. If not, the CPU will recognize that the Stack and Data have collided and will halt.
- The Status register is an 8 bit register whose various bits are used as flags. Only three of these flags are used in the current implementation.
- Bit 0 is the Carry/Borrow Flag. Any arithmetic operation either sets or clears it depending on whether or not the result causes Q to overflow/underflow. It is a 1 if a carry/underflow occurred, and a 0 otherwise. If A or B overflows or underflows from the use of an increment or decrement instruction, this flag will also be set. Non-overflowing increments or decrements will also reset it.
@@ -79,24 +78,24 @@ It has seven registers:
| 30 | PSHQ | Stores Q into Data Memory at the location referenced by the Stack Pointer then decrements the Stack Pointer. |
| 31 | PSHA | Stores A into Data Memory at the location referenced by the Stack Pointer then decrements the Stack Pointer. |
| 32 | PSHB | Stores B into Data Memory at the location referenced by the Stack Pointer then decrements the Stack Pointer. |
| 33 | PSHD | Stores the Data Pointer to the stack, with the low byte on top. Increments the Stack Pointer by two. |
| 33 | PSHD | Stores the Data Pointer referenced by the next byte in Program Memory to the stack, with the low byte on top. Decrements the Stack Pointer by two. |
| 34 | POPA | Reads the location referenced by the Stack Pointer from Data Memory into A then increments the Stack Pointer. |
| 35 | POPB | Reads the location referenced by the Stack Pointer from Data Memory into B then increments the Stack Pointer. |
| 36 | POPD | Restores the Data Pointer from the stack, increments the Stack Pointer by two. |
| 36 | POPD | Restores the Data Pointer referenced by the next byte in Program Memory from the stack, increments the Stack Pointer by two. |
### Data Operations: 10 Instructions
| Hex Code | Mnemonic | Description |
| -- | ---- | -- |
| 40 | INCD | Increments the Data Pointer. |
| 41 | DECD | Decrements the Data Pointer. |
| 42 | LDA | Loads the byte referenced from Data Memory by the Data Pointer into A. |
| 43 | LDB | Loads the byte referenced from Data Memory by the Data Pointer into B. |
| 44 | STQ | Stores Q into the byte referenced by the Data Pointer in Data Memory. |
| 45 | STA | Stores A into the byte referenced by the Data Pointer in Data Memory. |
| 46 | STB | Stores B into the byte referenced by the Data Pointer in Data Memory. |
| 47 | SETD | Loads the next two bytes of Program Memory into the Data Pointer. |
| 48 | DPUP | Offset Data Pointer up by the value of the immediate next byte of Program Memory. |
| 49 | DPDN | Offset Data Pointer down by the value of the immediate next byte of Program Memory. |
| 40 | INCD | Increments the Data Pointer referenced by the next byte in Program Memory. |
| 41 | DECD | Decrements the Data Pointer referenced by the next byte in Program Memory. |
| 42 | LDA | Loads the byte referenced from Data Memory by the Data Pointer into A referenced by the next byte in Program Memory. |
| 43 | LDB | Loads the byte referenced from Data Memory by the Data Pointer into B referenced by the next byte in Program Memory. |
| 44 | STQ | Stores Q into the byte referenced by the Data Pointer in Data Memory referenced by the next byte in Program Memory. |
| 45 | STA | Stores A into the byte referenced by the Data Pointer in Data Memory referenced by the next byte in Program Memory. |
| 46 | STB | Stores B into the byte referenced by the Data Pointer in Data Memory referenced by the next byte in Program Memory. |
| 47 | SETD | Loads the next two bytes of Program Memory into the Data Pointer referenced by the next byte in Program Memory. |
| 48 | DPUP | Offset Data Pointer referenced by the next byte in Program Memory up by the value of the immediate byte after of Program Memory. |
| 49 | DPDN | Offset Data Pointer referenced by the next byte in Program Memory down by the value of the immediate byte after of Program Memory. |
### Output Operations: 3 Instructions