Call instructionsCall instructions are special because they require more than four cycles to execute since PC and F need to be saved to the Stack before branching; however, these long sequences are built from the same ET0, ET1 signals provided by the "Time Counter" (T-Counter).
Call instructions are always unconditional. They can be Direct, Indirect, Relative or Relative Indirect.
Direct Calls (Class 10)
The branch address is read into OR during the Fetch cycle.
[10][0][0R][PC], addr Example: CALL 0x03ff ; 0xa031, 0x03ff
Relative Calls (Class 11)
[11][0][0R][PC], off-set Example: CALLR 0x08 ; 0xb031, 0x08
Indirect and Relative Indirect Calls (Class 12)
These two addressing modes for CALL instructions are grouped together in Class 12 since they don't require an operand to be fetched. Field OTA indicates the addressing mode as following:
0: Indirect
1: Relative Indirect
The branch address is given by a general purpose register used as a pointer (p).
[12][0][p][PC] Example: CALLX d ; 0xc071
[12][1][p][PC] CALLRX d ; 0xc171
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