EM78156E
8-Bit Microcontroller with MASK ROM
Vdd
Vdd
R1
EM78156E
Q1
/RESET
R2
40K
Fig. 16 Circuit 2 for the Residue Voltage Protection
4.12 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 by 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.
If for some reasons, the specification of the instruction cycle is not suitable for certain
applications, try modifying the instruction as follows:
(A) Change one instruction cycle to consist of 4 oscillator periods.
(B) "JMP", "CALL", "RET", "RETL", "RETI", or the conditional skip ("JBS", "JBC", "JZ",
"JZA", "DJZ", "DJZA") commands which were tested to be true, are executed within
two instruction cycles. The instructions that are written to the program counter also
take two instruction cycles.
Case (A) is selected by the CODE Option bit, called CLK. One instruction cycle
consists of two oscillator clocks if CLK is low, and four oscillator clocks if CLK is high.
Note that once the 4 oscillator periods within one instruction cycle is selected as in
Case (A), the internal clock source to TCC should be CLK=Fosc/4, not Fosc/ 2 as
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 register can be regarded as general register. That is, the same instruction
can operate on I/O register.
Product Specification (V1.3) 07.29.2004
• 27
(This specification is subject to change without further notice)
ELAN [ ELAN MICROELECTRONICS CORP ]
