Locations shown below are relative to the start of flags, typically 0xFF00.
Bits not defined read as zero and writing values will not have an effect.
| 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | |
|---|---|---|---|---|---|---|---|---|
| Read/Write | R | R/W | R/W | R | ||||
| **Default ** | X | 1 | 1 | X | ||||
| Name | ReadAvailable | ReadBlock | Enabled | Available |
- 8-bit unsigned number
- Read/Write
- 8-bit unsigned number
- Read/Write
- 8-bit unsigned number
- Read/Write
- 8-bit unsigned number
- Read/Write
Faults can be caught and handled by specifying a jump location in FLTRH and FLTRL. This handler must clear FLTSYS/2, it may call RET to continue execution or jump elsewhere.
| 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | |
|---|---|---|---|---|---|---|---|---|
| Read/Write | R | R | R | R | R/W | R/W | ||
| **Default ** | X | X | X | X | X | 0 | ||
| Name | Memory Overflow | Stack Exceeded | Illegal Op | Undefined Op | Trip | Enabled |
If not enabled, the system will halt should a fault occur.
In a fault condition, only one type will be indicated.
Clearing Trip will clear status bits 3-8, it cannot be set.
If a second fault occurs before trip is cleared, the system will halt; this known as a double-fault.
Undefined Op indicates an operation that was unknown. Illegal Op indicates that the parameters to the operation were not valid.
Stack Exceeded Indicates that the stack either overflowed (PUSH or CALL when full) or underflowed (RET or POP when empty).
The high byte of the fault handler jump.
The low byte of the fault handler jump.
Flags here for logic/math results
Tape control and status