PIC16C76-10/JW Microchip Technology, PIC16C76-10/JW Datasheet - Page 66

• Manufacturer Part Number: PIC16C76-10/JW
• Description: 8-Bit CMOS Microcontrollers with A/D Converter
• Manufacturer: Microchip Technology

PIC16C7X
8.1
Timer mode is selected by clearing the TMR1CS
(T1CON<1>) bit. In this mode, the input clock to the
timer is F
(T1CON<2>) has no effect since the internal clock is
always in sync.
8.2
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/CCP2 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 stage is an asynchronous ripple-counter.
In this configuration, 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.
FIGURE 8-2:
DS30390E-page 66
Note 1: When the T1OSCEN bit is cleared, the inverter and feedback resistor are turned off. This eliminates power drain.
RC0/T1OSO/T1CKI
RC1/T1OSI/CCP2
2: The CCP2 module is not implemented in the PIC16C72.
3: For the PIC16C73 and PIC16C74, the Schmitt Trigger is not implemented in external clock mode.
Timer1 Operation in Timer Mode
Timer1 Operation in Synchronized
Counter Mode
Applicable Devices
72 73 73A 74 74A 76 77
Applicable Devices
72 73 73A 74 74A 76 77
OSC
Set flag bit
TMR1IF on
Overflow
/4. The synchronize control bit T1SYNC
TIMER1 BLOCK DIAGRAM
(2)
TMR1H
T1OSC
TMR1
TMR1L
Oscillator
Enable
T1OSCEN
(1)
(3)
Clock
Internal
F
OSC
TMR1ON
/4
on/off
TMR1CS
1
0
8.2.1
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 specifications, parameters 45, 46, and 47.
When a prescaler other than 1:1 is used, the external
clock input is divided by the asynchronous ripple-
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 specifica-
tions, parameters 40, 42, 45, 46, and 47.
T1CKPS1:T1CKPS0
T1SYNC
Prescaler
1, 2, 4, 8
EXTERNAL CLOCK INPUT TIMING FOR
SYNCHRONIZED COUNTER MODE
0
1
2
Synchronized
clock input
1997 Microchip Technology Inc.
Synchronize
SLEEP input
det