PIC16LF18854 Datasheet, PDF (404/668 Pages) Microchip Technology – C Compiler Optimized RISC Architecture

PIC16(L)F18856/76
27.0 TIMER0 MODULE
The Timer0 module is an 8/16-bit timer/counter with the
following features:
• 16-bit timer/counter
• 8-bit timer/counter with programmable period
• Synchronous or asynchronous operation
• Selectable clock sources
• Programmable prescaler (independent of
Watchdog Timer)
• Programmable postscaler
• Operation during Sleep mode
• Interrupt on match or overflow
• Output on I/O pin (via PPS) or to other peripherals
27.1 Timer0 Operation
Timer0 can operate as either an 8-bit timer/counter or
a 16-bit timer/counter. The mode is selected with the
T016BIT bit of the T0CON register.
When used with an internal clock source, the module is
a timer and increments on every instruction cycle.
When used with an external clock source, the module
can be used as either a timer or a counter and
increments on every rising edge of the external source.
27.1.1 16-BIT MODE
In normal operation, TMR0 increments on the rising
edge of the clock source. A 15-bit prescaler on the
clock input gives several prescale options (see
prescaler control bits, T0CKPS<3:0> in the T0CON1
register).
27.1.1.1 Timer0 Reads and Writes in 16-Bit
Mode
TMR0H is not the actual high byte of Timer0 in 16-bit
mode. It is actually a buffered version of the real high
byte of Timer0, which is neither directly readable nor
writable (see Figure 27-1). TMR0H is updated with the
contents of the high byte of Timer0 during a read of
TMR0L. This provides the ability to read all 16 bits of
Timer0 without having to verify that the read of the high
and low byte was valid, due to a rollover between
successive reads of the high and low byte.
Similarly, a write to the high byte of Timer0 must also
take place through the TMR0H Buffer register. The high
byte is updated with the contents of TMR0H when a
write occurs to TMR0L. This allows all 16 bits of Timer0
to be updated at once.
27.1.2 8-BIT MODE
In normal operation, TMR0 increments on the rising
edge of the clock source. A 15-bit prescaler on the
clock input gives several prescale options (see
prescaler control bits, T0CKPS<3:0> in the T0CON1
register).
The value of TMR0L is compared to that of the Period
buffer, a copy of TMR0H, on each clock cycle. When
the two values match, the following events happen:
• TMR0_out goes high for one prescaled clock
period
• TMR0L is reset
• The contents of TMR0H are copied to the period
buffer
In 8-bit mode, the TMR0L and TMR0H registers are
both directly readable and writable. The TMR0L
register is cleared on any device Reset, while the
TMR0H register initializes at FFh.
Both the prescaler and postscaler counters are cleared
on the following events:
• A write to the TMR0L register
• A write to either the T0CON0 or T0CON1
registers
• Any device Reset – Power-on Reset (POR),
MCLR Reset, Watchdog Timer Reset (WDTR) or
• Brown-out Reset (BOR)
27.1.3 COUNTER MODE
In Counter mode, the prescaler is normally disabled by
setting the T0CKPS bits of the T0CON1 register to
‘0000’. Each rising edge of the clock input (or the
output of the prescaler if the prescaler is used)
increments the counter by ‘1’.
27.1.4 TIMER MODE
In Timer mode, the Timer0 module will increment every
instruction cycle as long as there is a valid clock signal
and the T0CKPS bits of the T0CON1 register
(Register 27-2) are set to ‘0000’. When a prescaler is
added, the timer will increment at the rate based on the
prescaler value.
27.1.5 ASYNCHRONOUS MODE
When the T0ASYNC bit of the T0CON1 register is set
(T0ASYNC = ‘1’), the counter increments with each
rising edge of the input source (or output of the
prescaler, if used). Asynchronous mode allows the
counter to continue operation during Sleep mode
provided that the clock also continues to operate during
Sleep.
27.1.6 SYNCHRONOUS MODE
When the T0ASYNC bit of the T0CON1 register is clear
(T0ASYNC = 0), the counter clock is synchronized to
the system oscillator (FOSC/4). When operating in
Synchronous mode, the counter clock frequency
cannot exceed FOSC/4.
27.2 Clock Source Selection
The T0CS<2:0> bits of the T0CON1 register are used
to select the clock source for Timer0. Register 27-2
displays the clock source selections.
DS40001824A-page 404
Preliminary
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