PIC16F877T-20I/L Microchip Technology, PIC16F877T-20I/L Datasheet - Page 178

• Manufacturer Part Number: PIC16F877T-20I/L
• Description: IC MCU FLASH 8KX14 EE 44PLCC
• Manufacturer: Microchip Technology
• Series: PIC® 16Fr

Specifications of PIC16F877T-20I/L

• 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
• Program Memory Size: 14KB (8K x 14)
• Program Memory Type: FLASH
• 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
• Package / Case: 44-PLCC
• For Use With: DVA16XL441 - ADAPTER DEVICE ICE 44PLCC309-1040 - ADAPTER 44-PLCC ZIF TO 40-DIP309-1039 - ADAPTER 44-PLCC TO 40-DIP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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.