em78p257 ELAN Microelectronics Corp, em78p257 Datasheet - Page 67

• Manufacturer Part Number: em78p257
• Description: 8-bit Microcontroller
• Manufacturer: ELAN Microelectronics Corp

4.14 Instruction Set
This specification is subject to change without prior notice.
Table 33 The List of the Instruction Set of EM78P257A/B
0 0000 0000 0000
INSTRUCTION BINARY
2. Customer ID Register (Word 1)
• Bit 12~ 0: Customer’s ID code
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",
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 :
Case (A) is selected by the CODE Option bit, called CLKS. One instruction cycle consists of two oscillator clocks
if CLKS is low, and four oscillator clocks if CLKS is high.
Note that once 4 oscillator periods within one instruction cycle is selected under Case (A), the internal clock
source to TCC will be CLK=Fosc/4 (not Fosc/ 2) as illustrated in Fig.6.
In addition, the instruction set has the following features:
The symbol "R" represents a register designator that specifies which one of the registers (including operational
registers and general purpose registers) is to be utilized by the instruction. "b" represents a bit field designator that
selects the value for the bit which is located in the register "R", and affects the operation. "k" represents an 8 or
10-bit constant or literal value.
(A) Modify one instruction cycle to consist of 4 oscillator periods.
(B) Execute within two instruction cycles the "JMP", "CALL", "RET", "RETL", "RETI" commands, or
(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
the conditional skip ("JBS", "JBC", "JZ", "JZA", "DJZ", "DJZA") which were tested to be true. The
instructions that are written to the program counter, should also take two instruction cycles.
I/O register.
XXXXXXXXXXXXX
Bit12~Bit0
0000
HEX
MNEMONIC
NOP
67
No Operation
OPERATION
). In this case, the execution
STATUS AFFECTED
EM78P257
None
07.27.2004 (V1.4)
OTP ROM