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EM78P156E Datasheet PDF : 28 Pages
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EM78P156E
VI.12 Instruction Set
Each instruction in the instruction set is a 13-bit word divided into an OP code and one or more operands.
Normally, all instructions are executed within one single instruction cycle (one instruction consists of 2 oscillator
periods), unless the program counter is changed by instruction “MOV R2,A”, “ADD R2,A”, or instructions of arithmetic
or logic operation on R2 (e.g. “SUB R2,A”, “BS(C) R2,6”, “CLR R2”, ......). In this case, the execution takes two
instruction cycles.
Under some conditions, if the specification of the instruction cycle is not suitable for some applications, they can be
modified as follows:
(A) one instruction cycle consists of 4 oscillator periods.
(B) “JMP”, “CALL”, “RET”, “RETL”, “RETI”, and the conditional skip (“JBS”, “JBC”, “JZ”, “JZA”, “DJZ”,
“DJZA”) tested to be true are executed within two instruction cycles. The instructions that write to the program
counter also take two instruction cycles.
The Case (A) is selected by the CODE option bit, called CLKS. One instruction cycle consists of two oscillator
clocks if CLKS is low, and consists of four oscillator clocks if CLKS is high.
Note that once 4 oscillator periods within one instruction cycle is selected in Case (A), the internal clock source to
TCC is CLK=Fosc/4 instead of Fosc/ 2 that is shown in Fig.5.
In addition, the instruction set has the following features:
(1) Every bit of any register can be set, cleared or tested directly.
(2) The I/O registers can be regarded as general registers. That is, the same instruction can operate on I/O register.
The symbol “R” represents a register designator which specifies which one of the registers (including operational
registers and general-purpose registers) to be utilized by the instruction. The symbol “b” represents a bit field designator
which selects the number of the bit located in the register “R” affected by the operation. The symbol “k” represents an
8 or 10-bit constant or literal value.
* This specification is subject to be changed without notice. 8.11.1999
B3-23
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