参数资料
型号: PIC18F252-E/SO
厂商: Microchip Technology
文件页数: 79/134页
文件大小: 0K
描述: IC MCU CMOS 40MHZ 16K FLSH28SOIC
产品培训模块: Asynchronous Stimulus
标准包装: 27
系列: PIC® 18F
核心处理器: PIC
芯体尺寸: 8-位
速度: 40MHz
连通性: I²C,SPI,UART/USART
外围设备: 欠压检测/复位,LVD,POR,PWM,WDT
输入/输出数: 23
程序存储器容量: 32KB(16K x 16)
程序存储器类型: 闪存
EEPROM 大小: 256 x 8
RAM 容量: 1.5K x 8
电压 - 电源 (Vcc/Vdd): 4.2 V ~ 5.5 V
数据转换器: A/D 5x10b
振荡器型: 外部
工作温度: -40°C ~ 125°C
封装/外壳: 28-SOIC(0.295",7.50mm 宽)
包装: 管件
1997 Microchip Technology Inc.
DS30444E - page 49
PIC16C9XX
7.3.1
SWITCHING PRESCALER ASSIGNMENT
The prescaler assignment is fully under software con-
trol, i.e., it can be changed “on the y” during program
execution.
Note:
To avoid an unintended device RESET, the
following instruction sequence (shown in
Example 7-1) must be executed when
changing the prescaler assignment from
Timer0 to the WDT. This precaution must
be followed even if the WDT is disabled.
EXAMPLE 7-1:
CHANGING PRESCALER (TIMER0
→WDT)
To change prescaler from the WDT to the Timer0 mod-
ule use the precaution shown in Example 7-2.
EXAMPLE 7-2:
CHANGING PRESCALER (WDT
→TIMER0)
CLRWDT
;Clear WDT and prescaler
BSF
STATUS, RP0 ;Select Bank1
MOVLW
b'xxxx0xxx' ;Select TMR0, new prescale value and
MOVWF
OPTION_REG
;clock source
BCF
STATUS, RP0 ;Select Bank0
TABLE 7-1: REGISTERS ASSOCIATED WITH TIMER0
1)
BSF
STATUS, RP0
;Select Bank1
Lines 2 and 3 do NOT have to
be included if the nal desired
prescale value is other than 1:1.
If 1:1 is nal desired value, then
a temporary prescale value is
set in lines 2 and 3 and the nal
prescale value will be set in lines
10 and 11.
2)
MOVLW
b'xx0x0xxx'
;Select clock source and prescale value of
3)
MOVWF
OPTION_REG
;other than 1:1
4)
BCF
STATUS, RP0
;Select Bank0
5)
CLRF
TMR0
;Clear TMR0 and prescaler
6)
BSF
STATUS, RP1
;Select Bank1
7)
MOVLW
b'xxxx1xxx'
;Select WDT, do not change prescale value
8)
MOVWF
OPTION_REG
;
9)
CLRWDT
;Clears WDT and prescaler
10) MOVLW
b'xxxx1xxx'
;Select new prescale value and WDT
11) MOVWF
OPTION_REG
;
12) BCF
STATUS, RP0
;Select Bank0
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Value on
Power-on
Reset
Value on all
other resets
01h, 101h
TMR0
Timer0 module’s register
xxxx xxxx
uuuu uuuu
0Bh, 8Bh,
10Bh, 18Bh
INTCON
GIE
PEIE
T0IE
INTE
RBIE
T0IF
INTF
RBIF
0000 000x
0000 000u
81h, 181h
OPTION RBPU INTEDG
T0CS
T0SE
PSA
PS2
PS1
PS0
1111 1111
85h
TRISA
PORTA Data Direction Control Register
--11 1111
Legend: x = unknown, u = unchanged, - = unimplemented locations read as '0'. Shaded cells are not used by Timer0.
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