Bit | Symbol | Description |
0 | I | Enable interrupts. Set/cleared by user. Also cleared on servicing an interrupt/exception. |
1 | N | Set/cleared when result is negative/positive |
2 | Z | Set/cleared when result is zero/non-zero |
3 | V | Set/cleared when there was/was not an overflow |
4 | X | Set/cleared when there was a carry (not cleared on non-arithmetic operations so can be used for extended arithmetic) |
5 | C | Set/cleared when there was a carry |
6 | D | Controls division mode |
7 | U | User bit. May be used for conditional branches, the BUS and BUC instructions are provided for this. Does not otherwise affect, and is not affected by processor operation but must be set/cleared explicitly by user. |
8 | F0 | Sign of R0 at start. Used for signed multiplication and division. |
9 | F1 | Sign of R1 at start. Used for signed multiplication and division. |
10 | F2 | Set to indicate processing of RESET |
11 | F3 | Set during end of shift part of multiplication iteration. |
12 | F4 | Set to indicate division by zero. |
13 | F5 | Set to indicate exception processing. |
14 | F6 | Set to modify an operation. In particular to make SHIFT calculate WEIGHT. |
15 | - | not used |
© 2014-2016 James Newman.