參數(shù)資料
型號： PIC16C56A-20I/JW
元件分類： 微控制器/微處理器
英文描述： 8-BIT, UVPROM, 20 MHz, RISC MICROCONTROLLER, CDIP18
封裝： 0.300 INCH, WINDOWED, CERDIP-18
文件頁數(shù)： 83/158頁
文件大小： 1194K
代理商： PIC16C56A-20I/JW
PIC16C5X
DS30453C-page 30
Preliminary
2000 Microchip Technology Inc.
6.2
Prescaler
An 8-bit counter is available as a prescaler for the
Timer0 module, or as a postscaler for the Watchdog
Timer (WDT), respectively (Section 6.1.2). For simplic-
ity, this counter is being referred to as “prescaler”
throughout this data sheet. Note that the prescaler may
be used by either the Timer0 module or the WDT, but
not both. Thus, a prescaler assignment for the Timer0
module means that there is no prescaler for the WDT,
and vice-versa.
The PSA and PS<2:0> bits (OPTION<3:0>) determine
prescaler assignment and prescale ratio.
When assigned to the Timer0 module, all instructions
writing
to
the
TMR0
register
(e.g.,
CLRF 1,
MOVWF 1,
BSF 1,x,
etc.) will clear the prescaler.
When assigned to WDT, a CLRWDT instruction will clear
the prescaler along with the WDT. The prescaler is nei-
ther readable nor writable. On a RESET, the prescaler
contains all '0's.
6.2.1
SWITCHING PRESCALER ASSIGNMENT
The prescaler assignment is fully under software control
(i.e., it can be changed “on the fly” during program exe-
cution). To avoid an unintended device RESET, the fol-
lowing instruction sequence (Example 6-1) must be
executed when changing the prescaler assignment from
Timer0 to the WDT.
EXAMPLE 6-1:
CHANGING PRESCALER
(TIMER0
→WDT)
1.CLRWDT
;Clear WDT
2.CLRF
TMR0
;Clear TMR0 & Prescaler
3.MOVLW
'00xx1111’b
;These 3 lines (5, 6, 7)
4.OPTION
; are required only if
; desired
5.CLRWDT
;PS<2:0> are 000 or
;001
6.MOVLW
'00xx1xxx’b
;Set Postscaler to
7.OPTION
; desired WDT rate
To change prescaler from the WDT to the Timer0 mod-
ule, use the sequence shown in Example 6-2. This
sequence must be used even if the WDT is disabled. A
CLRWDT
instruction should be executed before switching
the prescaler.
EXAMPLE 6-2:
CHANGING PRESCALER
(WDT
→TIMER0)
CLRWDT
;Clear WDT and
;prescaler
MOVLW
'xxxx0xxx'
;Select TMR0, new
;prescale value and
;clock source
OPTION
FIGURE 6-6:
BLOCK DIAGRAM OF THE TIMER0/WDT PRESCALER
T0CKI
T0SE
pin
TCY ( = FOSC/4)
Sync
2
Cycles
TMR0 reg
8-bit Prescaler
8 - to - 1MUX
M
MUX
Watchdog
Timer
PSA
0
1
0
1
WDT
Time-Out
PS<2:0>
8
Note: T0CS, T0SE, PSA, PS<2:0> are bits in the OPTION register.
PSA
WDT Enable bit
0
1
0
1
Data Bus
8
PSA
T0CS
M
U
X
M
U
X
U
X
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PIC16C56AT-04/SO 功能描述:8位微控制器 -MCU 1.5KB 25 RAM 12 I/O 4 MHz SOIC18 RoHS:否 制造商:Silicon Labs 核心:8051 處理器系列:C8051F39x 數(shù)據(jù)總線寬度:8 bit 最大時鐘頻率:50 MHz 程序存儲器大小:16 KB 數(shù)據(jù) RAM 大小:1 KB 片上 ADC:Yes 工作電源電壓:1.8 V to 3.6 V 工作溫度范圍:- 40 C to + 105 C 封裝 / 箱體:QFN-20 安裝風格:SMD/SMT
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