Undocumented SDBD Behavior
From Intellivision Wiki
Need to put here:
- SDBD + indirect through R6: Seem to recall results in two stack reads from top of stack, and ultimately decrements stack pointer once.
- SDBD + indirect while using same register as register argument. (e.g. SDBD; ADD@ R4, R4) CPU uses an interesting blend of old, new register values.
- SDBD + direct: Need to dig up Carl Jr's description of the CPU's behavior here. It's an interesting blend of Direct and Indirect access modes.