PIC16F874-20/L Microchip Technology, PIC16F874-20/L Datasheet - Page 185

• Manufacturer Part Number: PIC16F874-20/L
• Description: IC MCU FLASH 4KX14 EE 44PLCC
• Manufacturer: Microchip Technology
• Series: PIC® 16Fr

Specifications of PIC16F874-20/L

• Core Size: 8-Bit
• Program Memory Size: 7KB (4K x 14)
• Core Processor: PIC
• Speed: 20MHz
• Connectivity: I²C, SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, POR, PWM, WDT
• Number Of I /o: 33
• Program Memory Type: FLASH
• Eeprom Size: 128 x 8
• Ram Size: 192 x 8
• Voltage - Supply (vcc/vdd): 4 V ~ 5.5 V
• Data Converters: A/D 8x10b
• Oscillator Type: External
• Operating Temperature: 0°C ~ 70°C
• Package / Case: 44-PLCC
• Controller Family/series: PIC16F
• No. Of I/o's: 33
• Eeprom Memory Size: 128Byte
• Ram Memory Size: 192Byte
• Cpu Speed: 20MHz
• No. Of Timers: 3
• Processor Series: PIC16F
• Core: PIC
• Data Bus Width: 8 bit
• Data Ram Size: 192 B
• Interface Type: MSSP, PSP, USART
• Maximum Clock Frequency: 20 MHz
• Number Of Programmable I/os: 33
• Number Of Timers: 3
• Operating Supply Voltage: 2 V to 5.5 V
• Maximum Operating Temperature: + 70 C
• Mounting Style: SMD/SMT
• 3rd Party Development Tools: 52715-96, 52716-328, 52717-734
• Development Tools By Supplier: PG164130, DV164035, DV244005, DV164005, PG164120, ICE2000, DM163022, DV164120
• Minimum Operating Temperature: 0 C
• On-chip Adc: 10 bit, 8 Channel
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: AC164309 - MODULE SKT FOR PM3 44PLCC444-1001 - DEMO BOARD FOR PICMICRO MCUDVA16XL441 - ADAPTER DEVICE ICE 44PLCC309-1040 - ADAPTER 44-PLCC ZIF TO 40-DIP309-1039 - ADAPTER 44-PLCC TO 40-DIPDV007003 - PROGRAMMER UNIVERSAL PROMATE II
• Lead Free Status / Rohs Status: Details

12.5
12.5.1
12.5.2
1997 Microchip Technology Inc.
External Clock Input Timing with Unsynchronized Clock
Reading and Writing Timer1 in Asynchronous Counter Mode
Timer1 Operation in Asynchronous Counter Mode
If T1SYNC (T1CON<2>) is set, the external clock input is not synchronized. The timer continues
to increment asynchronously to the internal phase clocks. The timer will continue to run during
SLEEP and can generate an interrupt on overflow which will wake-up the processor. However,
special precautions in software are needed to read/write the timer (Subsection
and Writing Timer1 in Asynchronous Counter
sleep, Timer1 can be used to implement a true real-time clock.
In asynchronous counter mode, Timer1 cannot be used as a time-base for capture or compare
operations.
If the T1SYNC control bit is set, the timer will increment completely asynchronously. The input
clock must meet certain minimum high time and low time requirements. Refer to the Device Data
Sheet Electrical Specifications Section, timing
Reading TMR1H or TMR1L while the timer is running from an external asynchronous clock, will
guarantee 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 contention 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, since two separate reads are required to read the
entire 16-bits.
register.
Example 12-1:
04FFh
0500h
0501h
0502h
TMR1
Example 12-1
Reading 16-bit Register Issues
READ TMR1L
Store in TMPL
READ TMR1H
Store in TMPH
Action
shows why this may not be a straight forward read of the 16-bit
Sequence 1
TMPH:TMPL
05FFh
xxFFh
xxFFh
xxxxh
Section 12. Timer1
parameters
Mode”). Since the counter can operate in
45, 46, and 47.
READ TMR1H
Store in TMPH
READ TMR1L
Store in TMPL
Action
Sequence 2
DS31012A-page 12-5
12.5.2 “Reading
TMPH:TMPL
0401h
04xxh
04xxh
xxxxh
12