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Clarified Carry Flag behavior.

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Anachronaut
2024-11-20 17:54:05 -05:00
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parent 4eedc20b04
commit 49fd342135
1 changed files with 5 additions and 5 deletions
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SplitBit Programming Manual.md
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@@ -29,7 +29,7 @@ It has seven registers:
- 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 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. - 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. - 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.
- Bit 1 is the Stack Collision Flag. It is set if the Data Pointer's value ever meets or exceeds the Stack Pointer's value. This condition also sets the Halt Flag. - Bit 1 is the Stack Collision Flag. It is set if the Data Pointer's value ever meets or exceeds the Stack Pointer's value. This condition also sets the Halt Flag.
- Bit 7 is the Halt Flag. It is set by the HALT instruction, or if there is a stack collision. - Bit 7 is the Halt Flag. It is set by the HALT instruction, or if there is a stack collision.
@@ -65,10 +65,10 @@ It has seven registers:
| -- | ---- | -- | | -- | ---- | -- |
| 20 | RSTA | Resets A to 0. | | 20 | RSTA | Resets A to 0. |
| 21 | RSTB | Resets B to 0. | | 21 | RSTB | Resets B to 0. |
| 22 | INCA | Adds 1 to A. | | 22 | INCA | Adds 1 to A. If it overflows, it sets the Carry Flag, otherwise, it resets it. |
| 23 | INCB | Adds 1 to B. | | 23 | INCB | Adds 1 to B. If it overflows, it sets the Carry Flag, otherwise, it resets it. |
| 24 | DECA | Subtracts 1 from A. | | 24 | DECA | Subtracts 1 from A. If it underflows, it sets the Carry Flag, otherwise, it resets it. |
| 25 | DECB | Subtracts 1 from B. | | 25 | DECB | Subtracts 1 from B. If it underflows, it sets the Carry Flag, otherwise, it resets it. |
| 26 | INIA | Loads the next byte of Program Memory to A. | | 26 | INIA | Loads the next byte of Program Memory to A. |
| 27 | INIB | Loads the next byte of Program Memory to B. | | 27 | INIB | Loads the next byte of Program Memory to B. |
| 28 | CCF | Clears the Carry Flag. | | 28 | CCF | Clears the Carry Flag. |