PIC16F819-I/SO Microchip Technology Inc., PIC16F819-I/SO Datasheet - Page 61

• Manufacturer Part Number: PIC16F819-I/SO
• Description: 18 PIN, 3.5 KB FLASH, 256 RAM, 16 I/O
• Manufacturer: Microchip Technology Inc.

Specifications of PIC16F819-I/SO

• A/d Inputs: 5-Channel, 10-Bit
• Cpu Speed: 5 MIPS
• Eeprom Memory: 256 Bytes
• Input Output: 16
• Interface: I2C/SPI
• Memory Type: Flash
• Number Of Bits: 8
• Package Type: 18-pin SOIC
• Programmable Memory: 3.5K Bytes
• Ram Size: 256 Bytes
• Speed: 20 MHz
• Timers: 2-8-bit, 1-16-bit
• Voltage, Range: 2-5.5 V
• Lead Free Status / Rohs Status: RoHS Compliant part Electrostatic Device

7.5
If control bit, T1SYNC (T1CON<2>), is set, the external
clock input is not synchronized. The timer continues to
increment asynchronous to the internal phase clocks.
The timer will continue to run during Sleep and can
generate an interrupt on overflow that will wake-up the
processor. However, special precautions in software
are needed to read/write the timer.
In Asynchronous Counter mode, Timer1 cannot be
used as a time base for capture or compare operations.
EXAMPLE 7-1:
EXAMPLE 7-2:
 2004 Microchip Technology Inc.
; All interrupts are disabled
CLRF
MOVLW
MOVWF
MOVLW
MOVWF
; Re-enable the Interrupt (if required)
CONTINUE
; All interrupts are disabled
MOVF
MOVWF
MOVF
MOVWF
MOVF
SUBWF
BTFSC
GOTO
; TMR1L may have rolled over between the read of the high and low bytes.
; Reading the high and low bytes now will read a good value.
MOVF
MOVWF
MOVF
MOVWF
CONTINUE
Timer1 Operation in
Asynchronous Counter Mode
TMR1H, W
TMPH
TMR1L, W
TMPL
TMR1H, W
TMPH, W
STATUS, Z
CONTINUE
TMR1H, W
TMPH
TMR1L, W
TMPL
TMR1L
HI_BYTE
TMR1H, F
LO_BYTE
TMR1H, F
WRITING A 16-BIT FREE RUNNING TIMER
READING A 16-BIT FREE RUNNING TIMER
; Read high byte
; Read low byte
; Read high byte
; Sub 1st read with 2nd read
; Is result = 0
; Good 16-bit read
; Read high byte
; Read low byte
; Re-enable the Interrupt (if required)
; Continue with your code
; Clear Low byte, Ensures no rollover into TMR1H
; Value to load into TMR1H
; Write High byte
; Value to load into TMR1L
; Write Low byte
; Continue with your code
7.5.1
Reading TMR1H or TMR1L while the timer is running
from an external asynchronous clock will ensure a valid
read (taken care of in hardware). However, the user
should keep in mind that reading the 16-bit timer in two
8-bit values itself poses certain problems, since the
timer may overflow between the reads.
For writes, it is recommended that the user simply stop
the timer and write the desired values. A write conten-
tion may occur by writing to the timer registers while the
register is incrementing. This may produce an
unpredictable value in the timer register.
Reading the 16-bit value requires some care. The
example
Example 7-2 demonstrate how to write to and read
Timer1 while it is running in Asynchronous mode.
codes
READING AND WRITING TIMER1
IN ASYNCHRONOUS COUNTER
MODE
PIC16F818/819
provided
in
Example 7-1
DS39598E-page 59
and