PIC12F519 Microchip Technology, PIC12F519 Datasheet - Page 31

• Manufacturer Part Number: PIC12F519
• Description: 8-Bit Flash Microcontroller
• Manufacturer: Microchip Technology

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7.0
The Timer0 module has the following features:
• 8-bit timer/counter register, TMR0
• Readable and writable
• 8-bit software programmable prescaler
• Internal or external clock select:
Figure 7-1 is a simplified block diagram of the Timer0
module.
Timer mode is selected by clearing the T0CS bit
(OPTION<5>). In Timer mode, the Timer0 module will
increment every instruction cycle (without prescaler). If
TMR0 register is written, the increment is inhibited for
the following two cycles (Figure 7-2 and Figure 7-3).
The user can work around this by writing an adjusted
value to the TMR0 register.
FIGURE 7-1:
FIGURE 7-2:
© 2007 Microchip Technology Inc.
PC
(Program
Counter)
Instruction
Timer0
Instruction
Executed
Fetch
- Edge select for external clock
Note 1: Bits T0CS, T0SE, PSA, PS2, PS1 and PS0 are located in the OPTION register.
TIMER0 MODULE AND TMR0
REGISTER
T0CKI
2: The prescaler is shared with the Watchdog Timer.
pin
Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4
T0
PC – 1
T0SE
TIMER0 BLOCK DIAGRAM
TIMER0 TIMING: INTERNAL CLOCK/NO PRESCALE
F
(1)
MOVWF TMR0 MOVF TMR0,W MOVF TMR0,W MOVF TMR0,W MOVF TMR0,W MOVF TMR0,W
OSC
T0 + 1
/4
PC
T0CS
0
1
Write TMR0
executed
T0 + 2
PC + 1
(1)
PS2, PS1, PS0
Programmable
Prescaler
Preliminary
Read TMR0
reads NT0
PC + 2
3
(2)
(1)
Counter mode is selected by setting the T0CS bit
(OPTION<5>). In this mode, Timer0 will increment
either on every rising or falling edge of pin T0CKI. The
T0SE bit (OPTION<4>) determines the source edge.
Clearing the T0SE bit selects the rising edge. Restric-
tions on the external clock input are discussed in detail
in Section 7.1 “Using Timer0 with an External
Clock”.
The prescaler may be used by either the Timer0
module or the Watchdog Timer, but not both. The
prescaler assignment is controlled in software by the
control bit, PSA (OPTION<3>). Clearing the PSA bit
will assign the prescaler to Timer0. The prescaler is not
readable or writable. When the prescaler is assigned to
the Timer0 module, prescale values of 1:2, 1:4,...,
1:256 are selectable. Section 7.2 “Prescaler” details
the operation of the prescaler.
A summary of registers associated with the Timer0
module is found in Table 7-1.
The Timer0 contained in the CPU core follows the
standard baseline definition.
NT0
Read TMR0
reads NT0
PSA
1
0
PC + 3
PSout
(1)
(2 cycle delay)
Sync with
Read TMR0
reads NT0
Internal
Clocks
PC + 4
PSout
Sync
NT0 + 1
PIC12F519
Read TMR0
reads NT0 + 1
PC + 5
TMR0 Reg
Data Bus
DS41319A-page 29
Read TMR0
reads NT0 + 2
NT0 + 2
8
PC + 6