參數(shù)資料
型號： PIC16F818
廠商： Microchip Technology Inc.
英文描述： 18/20-Pin Enhanced FLASH Microcontrollers with nanoWatt Technology(18/20引腳，納瓦技術增強FLASH微控制器)
中文描述： 18/20-Pin增強型閃存微控制器采用納瓦技術（18/20引腳，納瓦技術增強閃存微控制器）
文件頁數(shù)： 56/164頁
文件大小： 3045K
代理商： PIC16F818
PIC16F818/819
DS39598C-page 54
Preliminary
2002 Microchip Technology Inc.
6.3
Using Timer0 with an External
Clock
When no prescaler is used, the external clock input is
the same as the prescaler output. The synchronization
of T0CKI, with the internal phase clocks, is accom-
plished by sampling the prescaler output on the Q2 and
Q4 cycles of the internal phase clocks. Therefore, it is
necessary for T0CKI to be high for at least 2 T
OSC
(and
a small RC delay of 20 ns) and low for at least 2 T
OSC
(and a small RC delay of 20 ns). Refer to the electrical
specification of the desired device.
6.4
Prescaler
There is only one prescaler available, which is mutually
exclusively shared between the Timer0 module and the
Watchdog Timer. A prescaler assignment for the
Timer0 module means that there is no prescaler for the
Watchdog Timer, and vice-versa. This prescaler is not
readable or writable (see Figure 6-1).
The PSA and PS2:PS0 bits (OPTION<3:0>) determine
the 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 Watchdog Timer. The
prescaler is not readable or writable.
REGISTER 6-1:
OPTION_REG REGISTER
Note:
Writing to TMR0 when the prescaler is
assigned to Timer0, will clear the prescaler
count but will not change the prescaler
assignment.
R/W-1
R/W-1
R/W-1
R/W-1
R/W-1
R/W-1
R/W-1
R/W-1
RBPU
bit 7
INTEDG
T0CS
T0SE
PSA
PS2
PS1
PS0
bit 0
bit 7
bit 6
bit 5
RBPU
INTEDG
T0CS
: TMR0 Clock Source Select bit
1
= Transition on T0CKI pin
0
= Internal instruction cycle clock (CLKO)
T0SE
: TMR0 Source Edge Select bit
1
= Increment on high-to-low transition on T0CKI pin
0
= Increment on low-to-high transition on T0CKI pin
PSA
: Prescaler Assignment bit
1
= Prescaler is assigned to the WDT
0
= Prescaler is assigned to the Timer0 module
PS2:PS0
: Prescaler Rate Select bits
Bit Value
TMR0 Rate WDT Rate
bit 4
bit 3
bit 2-0
Legend:
R = Readable bit
- n = Value at POR
W = Writable bit
‘1’ = Bit is set
U = Unimplemented bit, read as ‘0’
‘0’ = Bit is cleared
x = Bit is unknown
Note:
To avoid an unintended device RESET, the instruction sequence shown in the
PICmicro Mid-Range MCU Family Reference Manual (DS33023) must be exe-
cuted when changing the prescaler assignment from Timer0 to the WDT. This
sequence must be followed even if the WDT is disabled.
000
001
010
011
100
101
110
111
1 : 2
1 : 4
1 : 8
1 : 16
1 : 32
1 : 64
1 : 128
1 : 256
1 : 1
1 : 2
1 : 4
1 : 8
1 : 16
1 : 32
1 : 64
1 : 128
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PIC16F818-E/P 功能描述:8位微控制器 -MCU 1.75KB 128RAM 16 I/O Ext Temp PDIP18 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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