參數(shù)資料
型號(hào): P12C508
廠商: Microchip Technology Inc.
英文描述: 8-Pin, 8-Bit CMOS Microcontroller
中文描述: 8引腳,8位CMOS微控制器
文件頁數(shù): 10/84頁
文件大?。?/td> 526K
代理商: P12C508
PIC12C5XX
DS40139A-page 10
Advance Information
1996 Microchip Technology Inc.
3.1
Clocking Scheme/Instruction Cycle
The clock input (OSC1/CLKIN pin) is internally divided
by four to generate four non-overlapping quadrature
clocks namely Q1, Q2, Q3 and Q4. Internally, the
program counter is incremented every Q1, and the
instruction is fetched from program memory and
latched into instruction register in Q4. It is decoded
and executed during the following Q1 through Q4. The
clocks and instruction execution flow is shown in
Figure 3-2 and Example 3-1.
3.2
Instruction Flow/Pipelining
An Instruction Cycle consists of four Q cycles (Q1, Q2,
Q3 and Q4). The instruction fetch and execute are
pipelined such that fetch takes one instruction cycle
while decode and execute takes another instruction
cycle. However, due to the pipelining, each instruction
effectively executes in one cycle. If an instruction
causes the program counter to change (e.g.,
then two cycles are required to complete the
instruction (Example 3-1).
A fetch cycle begins with the program counter (PC)
incrementing in Q1.
In the execution cycle, the fetched instruction is
latched into the Instruction Register (IR) in cycle Q1.
This instruction is then decoded and executed during
the Q2, Q3, and Q4 cycles. Data memory is read
during Q2 (operand read) and written during Q4
(destination write).
GOTO
)
FIGURE 3-2:
CLOCK/INSTRUCTION CYCLE
EXAMPLE 3-1:
INSTRUCTION PIPELINE FLOW
Q1
Q2
Q3
Q4
Q1
Q2
Q3
Q4
Q1
Q2
Q3
Q4
OSC1
Q1
Q2
Q3
Q4
PC
OSC2
(RC mode)
PC
PC+1
PC+2
Fetch INST (PC)
Execute INST (PC-1)
Fetch INST (PC+1)
Execute INST (PC)
Fetch INST (PC+2)
Execute INST (PC+1)
Internal
phase
clock
All instructions are single cycle, except for any program branches. These take two cycles since the fetch
instruction is “flushed” from the pipeline while the new instruction is being fetched and then executed.
1. MOVLW 03H
Fetch 1
Execute 1
Fetch 2
2. MOVWF GPIO
Execute 2
Fetch 3
3. CALL SUB_1
Execute 3
Fetch 4
4. BSF GPIO, BIT1
Flush
Fetch SUB_1 Execute SUB_1
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