参数资料
型号: PIC18F252-E/SO
厂商: Microchip Technology
文件页数: 83/134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
PIC16C9XX
DS30444E - page 52
1997 Microchip Technology Inc.
8.1
Timer1 Operation in Timer Mode
Timer mode is selected by clearing the TMR1CS
(T1CON<1>) bit. In this mode, the input clock to the
timer is Fosc/4. The synchronize control bit T1SYNC
(T1CON<2>) has no effect since the internal clock is
always in sync.
8.2
Timer1 Operation in Synchronized
Counter Mode
Counter mode is selected by setting bit TMR1CS. In
this mode the timer increments on every rising edge of
clock input on pin RC1/T1OSI when bit T1OSCEN is
set or pin RC0/T1OSO/T1CKI when bit T1OSCEN is
cleared.
If T1SYNC is cleared, then the external clock input is
synchronized with internal phase clocks. The synchro-
nization is done after the prescaler stage. The pres-
caler is an asynchronous ripple-counter.
In this conguration, during SLEEP mode, Timer1 will
not increment even if the external clock is present,
since the synchronization circuit is shut off. The pres-
caler however will continue to increment.
8.2.1
EXTERNAL CLOCK INPUT TIMING FOR
SYNCHRONIZED COUNTER MODE
When an external clock input is used for Timer1 in syn-
chronized counter mode, it must meet certain require-
ments. The external clock requirement is due to
internal phase clock (Tosc) synchronization. Also, there
is a delay in the actual incrementing of TMR1 after syn-
chronization.
When the prescaler is 1:1, the external clock input is
the same as the prescaler output. The synchronization
of T1CKI 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 T1CKI to be high for at least 2Tosc (and
a small RC delay of 20 ns) and low for at least 2Tosc
(and a small RC delay of 20 ns). Refer to the appropri-
ate electrical specications, parameters 45, 46, and 47.
When a prescaler other than 1:1 is used, the external
clock input is divided by the asynchronous rip-
ple-counter type prescaler so that the prescaler output
is symmetrical. In order for the external clock to meet
the sampling requirement, the ripple-counter must be
taken into account. Therefore, it is necessary for T1CKI
to have a period of at least 4Tosc (and a small RC delay
of 40 ns) divided by the prescaler value. The only
requirement on T1CKI high and low time is that they do
not violate the minimum pulse width requirements of
10 ns). Refer to the appropriate electrical specica-
tions, parameters 40, 42, 45, 46, and 47.
FIGURE 8-2:
TIMER1 BLOCK DIAGRAM
TMR1H
TMR1L
T1OSC
T1SYNC
TMR1CS
T1CKPS1:T1CKPS0
SLEEP input
T1OSCEN
Enable
Oscillator(1)
Fosc/4
Internal
Clock
TMR1ON
on/off
Prescaler
1, 2, 4, 8
Synchronize
det
1
0
1
Synchronized
clock input
2
RC0/T1OSO/T1CKI
RC1/T1OSI
Note
1: When the T1OSCEN bit is cleared, the inverter and feedback resistor are turned off. This eliminates power drain.
Set ag bit
TMR1IF on
Overow
TMR1
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