PIC16F877A-I/ML Microchip Technology, PIC16F877A-I/ML Datasheet - Page 154

• Manufacturer Part Number: PIC16F877A-I/ML
• Description: IC MCU FLASH 8KX14 A/D 44QFN
• Manufacturer: Microchip Technology
• Series: PIC® 16Fr

Specifications of PIC16F877A-I/ML

• Core Size: 8-Bit
• Program Memory Size: 14KB (8K 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: 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-QFN
• Controller Family/series: PIC16F
• No. Of I/o's: 33
• Eeprom Memory Size: 256Byte
• Ram Memory Size: 368Byte
• Cpu Speed: 20MHz
• No. Of Timers: 3
• Processor Series: PIC16F
• Core: PIC
• Data Bus Width: 8 bit
• Data Ram Size: 368 B
• Interface Type: I2C, SPI, USART
• Maximum Clock Frequency: 20 MHz
• Number Of Programmable I/os: 33
• Number Of Timers: 1 x 16 bit
• 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: PG164130, DV164035, DV244005, DV164005, PG164120, ICE2000, DM163022, DV164120
• Minimum Operating Temperature: - 40 C
• On-chip Adc: 8
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: XLT44QFN2 - SOCKET TRAN ICE 44QFN/40DIPAC164322 - MODULE SOCKET MPLAB PM3 28/44QFN444-1001 - DEMO BOARD FOR PICMICRO MCU
• Lead Free Status / Rohs Status: Details

PICmicro MID-RANGE MCU FAMILY
9.10
9.10.1
DS31009A-page 9-14
Bi-directional I/O Ports
I/O Programming Considerations
When using the ports (and GPIO) as I/O, design considerations need to be taken into account to
ensure that the operation is as intended.
Any instruction which performs a write operation actually does a read followed by a write opera-
tion. The BCF and BSF instructions, for example, read the register into the CPU, execute the bit
operation, and write the result back to the register. Caution must be used when these instructions
are applied to a port with both inputs and outputs defined. For example, a BSF operation on bit5
of PORTB will cause all eight bits of PORTB to be read into the CPU. Then the BSF operation
takes place on bit5 and PORTB is written to the output latches. If another bit of PORTB is used
as a bi-directional I/O pin (e.g., bit0) and it is defined as an input at this time, the input signal
present on the pin itself would be read into the CPU and rewritten to the data latch of this partic-
ular pin, overwriting the previous content. As long as the pin stays in the input mode, no problem
occurs. However, if bit0 is switched to an output, the content of the data latch may now be
unknown.
Reading the port register, reads the values of the port pins. Writing to the port register writes the
value to the port latch. When using read-modify-write instructions (ex. BCF, BSF, etc.) on a port,
the value of the port pins is read, the desired operation is performed on this value, and the value
is then written to the port latch.
Example 9-9
Example 9-9: Read-Modify-Write Instructions on an I/O Port
A pin configured as an output, actively driving a Low or High should not be driven from external
devices at the same time in order to change the level on this pin (“wired-or,” “wired-and”). The
resulting high output currents may damage the chip.
; Initial PORT settings: PORTB<7:4> Inputs
;
; PORTB<7:6> have external pull-ups and are not connected to other circuitry
;
;
;
;
; Note that the user may have expected the pin values to be 00pp ppp.
; The 2nd BCF caused RB7 to be latched as the pin value (high).
BCF
BCF
BSF
BCF
BCF
PORTB, 7
PORTB, 6
STATUS, RP0
TRISB, 7
TRISB, 6
shows the effect of two sequential read-modify-write instructions on an I/O port.
; 01pp pppp
; 10pp pppp
;
; 10pp pppp
; 10pp pppp
PORT latch
----------
PORTB<3:0> Outputs
PORT pins
---------
11pp pppp
11pp pppp
11pp pppp
10pp pppp
1997 Microchip Technology Inc.