參數(shù)資料
型號: 16F84
廠商: Microchip Technology Inc.
英文描述: CAT 5E CROSSOVER, BLUE 15 FT PATCH CABLE
中文描述: 18引腳閃存/ EEPROM的8位微控制器
文件頁數(shù): 27/124頁
文件大小: 1322K
代理商: 16F84
PIC16F8X
1998 Microchip Technology Inc.
DS30430C-page 27
6.0
TIMER0 MODULE AND TMR0
REGISTER
The Timer0 module timer/counter has the following
features:
8-bit timer/counter
Readable and writable
8-bit software programmable prescaler
Internal or external clock select
Interrupt on overflow from FFh to 00h
Edge select for external clock
Timer mode is selected by clearing the T0CS bit
(OPTION_REG<5>). In timer mode, the Timer0 mod-
ule (Figure 6-1) will increment every instruction cycle
(without prescaler). If the TMR0 register is written, the
increment is inhibited for the following two cycles
(Figure 6-2 and Figure 6-3). The user can work around
this by writing an adjusted value to the TMR0 register.
Counter mode is selected by setting the T0CS bit
(OPTION_REG<5>). In this mode TMR0 will increment
either on every rising or falling edge of pin RA4/T0CKI.
The incrementing edge is determined by the T0 source
edge select bit, T0SE (OPTION_REG<4>). Clearing bit
T0SE selects the rising edge. Restrictions on the exter-
nal clock input are discussed in detail in Section 6.2.
The prescaler is shared between the Timer0 Module
and the Watchdog Timer. The prescaler assignment is
controlled,
in
software,
(OPTION_REG<3>). Clearing bit PSA will assign the
prescaler to the Timer0 Module. The prescaler is not
readable or writable. When the prescaler (Section 6.3)
is assigned to the Timer0 Module, the prescale value
(1:2, 1:4, ..., 1:256) is software selectable.
by
control
bit
PSA
6.1
TMR0 Interrupt
The TMR0 interrupt is generated when the TMR0
register overflows from FFh to 00h. This overflow sets
the T0IF bit (INTCON<2>). The interrupt can be
masked by clearing enable bit T0IE (INTCON<5>). The
T0IF bit must be cleared in software by the Timer0
Module interrupt service routine before re-enabling this
interrupt. The TMR0 interrupt (Figure 6-4) cannot wake
the processor from SLEEP since the timer is shut off
during SLEEP.
FIGURE 6-1:
TMR0 BLOCK DIAGRAM
FIGURE 6-2:
TMR0 TIMING: INTERNAL CLOCK/NO PRESCALER
Note 1:
Bits T0CS, T0SE, PS2, PS1, PS0 and PSA are located in the OPTION_REG register.
2:
The prescaler is shared with the Watchdog Timer (Figure 6-6)
RA4/T0CKI
pin
T0SE
0
1
1
0
T0CS
F
OSC
/4
Programmable
Prescaler
Sync with
Internal
clocks
TMR0 register
PSout
(2 cycle delay)
PSout
Data bus
8
Set bit T0IF
on Overflow
PSA
PS2, PS1, PS0
3
PC-1
Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4
PC
InstrFetch
TMR0
PC
PC+1
PC+2
PC+3
PC+4
PC+5
PC+6
T0
T0+1
T0+2
NT0
NT0
NT0
NT0+1
NT0+2
T0
MOVWF TMR0
MOVF TMR0,W
MOVF TMR0,W
MOVF TMR0,W
MOVF TMR0,W
MOVF TMR0,W
Write TMR0
executed
Read TMR0
Read TMR0
Read TMR0
Read TMR0
reads NT0 + 1
Read TMR0
Instruction
Executed
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