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Instruction Set
3-72
RISC 16−Bit CPU
3.4.4 Instruction Cycles and Lengths
The number of CPU clock cycles required for an instruction depends on the
instruction format and the addressing modes used - not the instruction itself.
The number of clock cycles refers to the MCLK.
Interrupt and Reset Cycles
Table 3−14 lists the CPU cycles for interrupt overhead and reset.
Table 3−14.Interrupt and Reset Cycles
No. of
Cycles
Length of
Action
No. of
Cycles
Length of
Instruction
Return from interrupt (RETI)
5 1
Interrupt accepted 6 −
WDT reset 4 −
Reset (RST/NMI) 4 −
Format-II (Single Operand) Instruction Cycles and Lengths
Table 3−15 lists the length and CPU cycles for all addressing modes of
format-II instructions.
Table 3−15.Format-II Instruction Cycles and Lengths
No. of Cycles
Addressing
Mode
RRA, RRC
SWPB, SXT
PUSH CALL
Length of
Instruction
Example
Rn 1 3 4 1 SWPB R5
@Rn 3 4 4 1 RRC @R9
@Rn+ 3 5 5 1 SWPB @R10+
#N (See note) 4 5 2 CALL #0F000h
X(Rn) 4 5 5 2 CALL 2(R7)
EDE 4 5 5 2 PUSH EDE
&EDE
4 5 5 2 SXT &EDE
Note: Instruction Format II Immediate Mode
Do not use instructions RRA, RRC, SWPB, and SXT with the immediate
mode in the destination field. Use of these in the immediate mode results in
an unpredictable program operation.
Format-III (Jump) Instruction Cycles and Lengths
All jump instructions require one code word, and take two CPU cycles to
execute, regardless of whether the jump is taken or not.