PIC16F877A-I/P Microchip Technology, PIC16F877A-I/P Datasheet - Page 178

• Manufacturer Part Number: PIC16F877A-I/P
• Description: IC MCU FLASH 8KX14 EE 40DIP
• Manufacturer: Microchip Technology
• Series: PIC® 16Fr

Specifications of PIC16F877A-I/P

• Program Memory Type: FLASH
• Program Memory Size: 14KB (8K x 14)
• Package / Case: 40-DIP (0.600", 15.24mm)
• Core Processor: PIC
• Core Size: 8-Bit
• Speed: 20MHz
• Connectivity: I²C, SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, POR, PWM, WDT
• Number Of I /o: 33
• Eeprom Size: 256 x 8
• Ram Size: 368 x 8
• Voltage - Supply (vcc/vdd): 4 V ~ 5.5 V
• Data Converters: A/D 8x10b
• Oscillator Type: External
• Operating Temperature: -40°C ~ 85°C
• Processor Series: PIC16F
• Core: PIC
• Data Bus Width: 8 bit
• Data Ram Size: 368 B
• Interface Type: CCP/I2C/MSSP/SPI/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: + 85 C
• Mounting Style: Through Hole
• 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: - 40 C
• On-chip Adc: 8-ch x 10-bit
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: 444-1001 - DEMO BOARD FOR PICMICRO MCU
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: PIC16F877AI/P

PICmicro MID-RANGE MCU FAMILY
11.7
DS31011A-page 11-10
Design Tips
Question 1:
Answer 1:
If you are polling TMR0 to see if it has rolled over to zero. You could do this by executing:
wait
Two possible scenarios to lose clock cycles are:
1.
2.
If you are incrementing TMR0 from the internal instruction clock, or an external source that
is about as fast, the overflow could occur during the two cycle GOTO, so you could miss it.
In this case the TMR0 source should be prescaled.
Or you could do a test to see if it has rolled over by checking for less than a nominal value:
When writing to TMR0, two instruction clock cycles are lost. Often you have a specific time
period you want to count, say 100 decimal. In that case you might put 156 into TMR0
(256 - 100 = 156). However, since two instruction cycles are lost when you write to TMR0
(for internal logic synchronization), you should actually write 158 to the timer.
Wait
MOVF
BTFSS
GOTO
movlw
subwf
btfsc
goto
I am implementing a counter/clock, but the clock loses time or is
inaccurate.
TMR0,W
STATUS,Z
wait
3
TMR0,W
STATUS,C
Wait
; read the timer into W
; see if it was zero, if so,
;
; if not zero yet, keep waiting
break from loop
1997 Microchip Technology Inc.