PIC16C621A Microchip Technology Inc., PIC16C621A Datasheet - Page 36

• Manufacturer Part Number: PIC16C621A
• Description: Eprom-based 8-bit Cmos Microcontrollers
• Manufacturer: Microchip Technology Inc.

PIC16C62X
6.3
An 8-bit counter is available as a prescaler for the
Timer0 module, or as a postscaler for the Watchdog
Timer, respectively (Figure 6-6). For simplicity, this
counter is being referred to as “prescaler” throughout
this data sheet. Note that there is only one prescaler
available which is mutually exclusive between the
Timer0 module and the Watchdog Timer. Thus, a
prescaler assignment for the Timer0 module means
that there is no prescaler for the Watchdog Timer and
vice-versa.
FIGURE 6-6:
DS30235J-page 34
CLKOUT (= Fosc/4)
WDT Enable bit
Note: T0SE, T0CS, PSA, PS<2:0> are bits in the OPTION register.
T0CKI
Watchdog
pin
Timer
Prescaler
T0SE
BLOCK DIAGRAM OF THE TIMER0/WDT PRESCALER
0
1
PSA
M
U
X
0
1
T0CS
M
U
X
0
8-bit Prescaler
8-to-1MUX
Time-out
8
M U X
WDT
1
0
1
PSA
M
U
X
The PSA and PS<2:0> bits (OPTION<3:0>) determine
the prescaler assignment and prescale ratio.
When assigned to the Timer0 module, all instructions
writing
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.
PSA
PS<2:0>
to
Cycles
SYNC
2
the
TMR0
 2003 Microchip Technology Inc.
TMR0 reg
register
Data Bus
8
(e.g.,
Set flag bit T0IF
on Overflow
CLRF 1,