參數(shù)資料
型號: μPD789801
廠商: NEC Corp.
英文描述: 8 Bit Single Chip Microcontrollers(8位單片微控制器)
中文描述: 8位單片機(jī)微控制器(8位單片微控制器)
文件頁數(shù): 30/125頁
文件大?。?/td> 366K
代理商: ΜPD789801
CHAPTER 3 ADDRESSING
13
CHAPTER 3 ADDRESSING
3.1 INSTRUCTION ADDRESS ADDRESSING
An instruction address is determined by program counter (PC) contents. PC contents are normally incremented
(+1 for each byte) automatically according to the number of bytes of an instruction to be fetched each time another
instruction is executed. When a branch instruction is executed, the branch destination information is set in the PC
and branched by the following addressing (For details of each instruction, see
Chapter 5
).
3.1.1 Relative Addressing
[Function]
The value obtained by adding 8-bit immediate data (displacement value: jdisp8) of an instruction code to the
start address of the following instruction is transferred to the program counter (PC) and branched. The
displacement value is treated as signed two’s complement data (-128 to +127) and bit 7 becomes a sign bit.
Thus, relative addressing causes a branch to an address within the range of -128 to +127, relative to the start
address of the next instruction.
This function is carried out when the BR $addr16 instruction or a conditional branch instruction is executed.
[Illustration]
15
0
PC
15
0
S
15
0
PC
+
8
7
6
α
jdisp8
When S = 0,
α
indicates all bits "0".
When S = 1,
α
indicates all bits "1".
... PC is the start address of
the next instruction of
a BR instruction.
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