PIC16F84A-20I/SS Microchip Technology, PIC16F84A-20I/SS Datasheet - Page 158

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

Specifications of PIC16F84A-20I/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: -40°C ~ 85°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
• Processor Series: PIC16F
• Core: PIC
• Data Bus Width: 8 bit
• Data Ram Size: 68 B
• Maximum Clock Frequency: 20 MHz
• Number Of Programmable I/os: 13
• Number Of Timers: 8
• Operating Supply Voltage: 2 V to 5.5 V
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• 3rd Party Development Tools: 52715-96, 52716-328, 52717-734
• Development Tools By Supplier: ICE2000
• Minimum Operating Temperature: - 40 C
• Data Rom Size: 64 B
• Height: 1.75 mm
• Length: 7.2 mm
• Supply Voltage (max): 5.5 V
• Supply Voltage (min): 4 V
• Width: 5.3 mm
• 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: Details

PICmicro MID-RANGE MCU FAMILY
DS31009A-page 9-18
Question 4:
Answer 4:
1.
2.
Another case where a read-modify-write instruction may seem to change other pin values
unexpectedly can be illustrated as follows: Suppose you make PORTC all outputs and
drive the pins low. On each of the port pins is an LED connected to ground, such that a
high output lights it. Across each LED is a 100 F capacitor. Let's also suppose that the
processor is running very fast, say 20 MHz. Now if you go down the port setting each pin
in order; BSF PORTC,0 then BSF PORTC,1 then BSF PORTC,2 and so on, you may see
that only the last pin was set, and only the last LED actually turns on. This is because the
capacitors take a while to charge. As each pin was set, the pin before it was not charged
yet and so was read as a zero. This zero is written back out to the port latch (r-m-w,
remember) which clears the bit you just tried to set the instruction before. This is usually
only a concern at high speeds and for successive port operations, but it can happen, so
take it into consideration.
If this is on a PIC16C7XX device, you have not configured the I/O pins properly in the
ADCON1 register. If a pin is configured for analog input, any read of that pin will read a
zero, regardless of the voltage on the pin. This is an exception to the normal rule that the
pin state is always read. You can still configure an analog pin as an output in the TRIS reg-
ister, and drive the pin high or low by writing to it, but you will always read a zero. Therefore
if you execute a Read-Modify-Write instruction (see previous question) all analog pins are
read as zero, and those not directly modified by the instruction will be written back to the
port latch as zero. A pin configured as analog is expected to have values that may be nei-
ther high nor low to a digital pin, or floating. Floating inputs on digital pins are a no-no, and
can lead to high current draw in the input buffer, so the input buffer is disabled.
When I perform a BCF instruction, other pins get cleared in the port. Why?
1997 Microchip Technology Inc.