KS57C2308/P2308/C2316/P2316 SAM47 INSTRUCTION SET
5-75
REF — Reference Instruction
REF dst
Operation: Operand Operation Summary Bytes Cycles
memc Reference code 11 (note)
NOTE:The instruction referenced by REF determines the instruction cycles.
Description: The REF instruction is used to rewrite into 1-byte form, arbitrary 2-byte or 3-byte instructions (or
two 1-byte instructions) stored in the REF instruction reference area in program memory. REF
reduces the number of program memory accesses for a program.
Operand Binary Code Operation Notation
memc t7 t6 t5 t4 t3 t2 t1 t0 PC13–0 ← memc.5–0 + (memc +
1).7–0
TJP and TCALL are 2-byte pseudo-instructions that are used only to specify the reference area:
1. When the reference area is specified by the TJP instruction,
memc.7–6 = 00
PC13–0 ← memc.5–0 + (memc + 1).7–0
2. When the reference area is specified by the TCALL instruction,
memc.7–6 = 01
(SP–4) (SP–1) (SP–2) ← PC12–0
SP–3 ← EMB, ERB, PC13–12
PC13–0 ← memc.5–0 + (memc + 1).7–0
SP ← SP–4
When the reference area is specified by any other instruction, the “memc” and “memc + 1”
instructions are executed.
Instructions referenced by REF occupy 2 bytes of memory space (for two 1-byte instructions or
one 2-byte instruction) and must be written as an even number from 0020H to 007FH in ROM. In
addition, the destination address of the TJP and TCALL instructions must be located with the
3FFFH address. TJP and TCALL are reference instructions for JP/JPS and CALL/CALLS.
If the instruction following a REF is subject to the “redundancy effect”, the redundant instruction
is skipped. If, however, the REF follows a redundant instruction, it is executed.
On the other hand, the binary code of a REF instruction is 1 byte. The upper 4 bits become the
higher address bits of the referenced instruction, and the lower 4 bits of the referenced instruction
becomes the lower address, producing a total of 8 bits or 1 byte (see Example 3 below).
NOTE
If the MSB value of the first one-byte binary code in instruction is “0”, the instruction cannot be
referenced by a REF instruction.