PIC16F84A-20/SS Microchip Technology, PIC16F84A-20/SS Datasheet - Page 178

• Manufacturer Part Number: PIC16F84A-20/SS
• Description: IC MCU FLASH 1KX14 EE 20SSOP
• Manufacturer: Microchip Technology
• Series: PIC® 16Fr

Specifications of PIC16F84A-20/SS

• Core Size: 8-Bit
• Program Memory Size: 1.75KB (1K x 14)
• Core Processor: PIC
• Speed: 20MHz
• Peripherals: POR, WDT
• Number Of I /o: 13
• Program Memory Type: FLASH
• Eeprom Size: 64 x 8
• Ram Size: 68 x 8
• Voltage - Supply (vcc/vdd): 4 V ~ 5.5 V
• Oscillator Type: External
• Operating Temperature: 0°C ~ 70°C
• Package / Case: 20-SSOP
• Controller Family/series: PIC16F
• No. Of I/o's: 13
• Eeprom Memory Size: 64Byte
• Ram Memory Size: 68Byte
• Cpu Speed: 20MHz
• No. Of Timers: 1
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: XLT20SS1-1 - SOCKET TRANSITION 20DIP 20SSOPI3-DB16F84A - BOARD DAUGHTER ICEPIC3AC164307 - MODULE SKT FOR PM3 28SSOPAC164018 - MODULE SKT PROMATEII 20SSOP
• Data Converters: -
• Connectivity: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, 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.