參數(shù)資料
型號: PIC16C620A-20/P301
元件分類: 微控制器/微處理器
英文描述: 8-BIT, OTPROM, 20 MHz, RISC MICROCONTROLLER, PDIP18
封裝: 0.300 INCH, PLASTIC, DIP-18
文件頁數(shù): 34/108頁
文件大?。?/td> 674K
代理商: PIC16C620A-20/P301
1998 Microchip Technology Inc.
Preliminary
DS30235G-page 31
PIC16C62X
6.0
TIMER0 MODULE
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 overow from FFh to 00h
Edge select for external clock
Figure 6-1 is a simplied block diagram of the Timer0
module.
Timer mode is selected by clearing the T0CS bit
(OPTION<5>). In timer mode, the TMR0 will increment
every instruction cycle (without prescaler). If Timer0 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 TMR0.
Counter mode is selected by setting the T0CS bit. In
this mode Timer0 will increment either on every rising
or falling edge of pin RA4/T0CKI. The incrementing
edge is determined by the source edge (T0SE) control
bit (OPTION<4>). Clearing the T0SE bit selects the
rising edge. Restrictions on the external 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
by
the
control
bit
PSA
(OPTION<3>). Clearing the PSA bit will assign the
prescaler to Timer0. The prescaler is not readable or
writable. When the prescaler is assigned to the Timer0
module, prescale value of 1:2, 1:4, ..., 1:256 are
selectable. Section 6.3 details the operation of the
prescaler.
6.1
TIMER0 Interrupt
Timer0 interrupt is generated when the TMR0 register
timer/counter overows from FFh to 00h. This overow
sets the T0IF bit. The interrupt can be masked by
clearing the T0IE bit (INTCON<5>). The T0IF bit
(INTCON<2>) must be cleared in software by the
Timer0
module
interrupt
service
routine
before
re-enabling this interrupt. The Timer0 interrupt cannot
wake the processor from SLEEP since the timer is shut
off during SLEEP. See Figure 6-4 for Timer0 interrupt
timing.
FIGURE 6-1:
TIMER0 BLOCK DIAGRAM
FIGURE 6-2:
TIMER0 (TMR0) TIMING: INTERNAL CLOCK/NO PRESCALER
Note 1:
Bits T0SE, T0CS, PS2, PS1, PS0 and PSA are located in the OPTION register.
2:
The prescaler is shared with Watchdog Timer (Figure 6-6)
RA4/T0CKI
T0SE
0
1
0
pin
T0CS
FOSC/4
Programmable
Prescaler
Sync with
Internal
clocks
TMR0
PSout
(2 TCY delay)
PSout
Data bus
8
Set Flag bit T0IF
on Overow
PSA
PS2:PS0
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
(Program
Counter)
Instruction
Fetch
TMR0
PC
PC+1
PC+2
PC+3
PC+4
PC+5
PC+6
T0
T0+1
T0+2
NT0
NT0+1
NT0+2
T0
MOVWF TMR0
MOVF TMR0,W
Write TMR0
executed
Read TMR0
reads NT0
Read TMR0
reads NT0
Read TMR0
reads NT0
Read TMR0
reads NT0 + 1
Read TMR0
reads NT0 + 2
Instruction
Executed
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