CHP 3

INPUT OUTPUT PORTS PROGRMMING

Lesson Learning Outcomes :

At the end of this topic, students should be able to:

Identify input and output (I/O) pins and their function

Code PIC instruction for I/O handling

Code I/O bit-manipulation programs for the PIC

Examine the bit addressability of PIC ports

Input and Output (I/O) pins

PIC18 Pin Diagram

Input and Output (I/O) pins

PIC18 has many ports Depending on the family member

Depending on the number of pins on the chip

Each port can be configured as input or output.

Bidirectional port Each port has some other functions

Such as timer , ADC, interrupts and serial communication.

Input and Output (I/O) pins

Each port has three registers for its operation. These registers are:

TRIS register (data direction register)

If the corresponding bit is 0 Output

If the corresponding bit is 1 Input

PORT register (reads the levels on the pins of the device)

LAT register (output latch)

Input and Output (I/O) pins

Consist of :

PORTA (RAx) - 6 pins PORTB (RBx) 8 pins PORTC (RCx) 7 pins PORTD (RDx) 8 pins PORTE (REx) 4 pins VUSB Vdd (Vcc) Vss (GND) OSC1,OSC2 MCLR( reset)

PORTA, TRISA and LATA Registers

PORTA is an 8-bit wide, bidirectional port.

The corresponding data direction register is TRISA.

Setting a TRISA bit (= 1) will make the corresponding PORTA pin an input

Clearing a TRISA bit (= 0) will make the corresponding PORTA pin an output.

The Data Latch register (LATA) is also memory

mapped.Useful for read-modify-write operations on the value driven by the I/O pins.

PORTA, TRISA and LATA Registers

Registers associated with Port A

Port A as Input

Port A as Output

PORT B, PORT C, PORT D and PORT E

PORTB is 8 pins

PORTC is 7 pins

PORTD is 8 pins

PORTE is 4 pins

PORTB, TRISB and LATB Registers

PORTB is an 8-bit wide, bidirectional port.

The corresponding data direction register is TRISB.

Setting a TRISB bit (= 1) will make the corresponding PORTB pin an input

Clearing a TRISB bit (= 0) will make the corresponding PORTB pin an output.

The Data Latch register (LATB) is also memory

mapped.Useful for read-modify-write operations on the value driven by the I/O pins.

PORTC, TRISC and LATC Registers

PORTC is an 7-bit wide, bidirectional port.

The corresponding data direction register is TRISC.

Setting a TRISC bit (= 1) will make the corresponding PORTC pin an input

Clearing a TRISC bit (= 0) will make the corresponding PORTC pin an output.

The Data Latch register (LATC) is also memory

mapped.Useful for read-modify-write operations on the value driven by the I/O pins.

PORTD, TRISD and LATD Registers

PORTD is an 7-bit wide, bidirectional port.

The corresponding data direction register is TRISD.

Setting a TRISD bit (= 1) will make the corresponding PORTD pin an input

Clearing a TRISD bit (= 0) will make the corresponding PORTD pin an output.

The Data Latch register (LATD) is also memory

mapped.Useful for read-modify-write operations on the value driven by the I/O pins.

PORTE, TRISE and LATE Registers

PORTE is an 4-bit wide, bidirectional port.

The corresponding data direction register is TRISE.

Setting a TRISE bit (= 1) will make the corresponding PORTE pin an input

Clearing a TRISE bit (= 0) will make the corresponding PORTE pin an output.

The Data Latch register (LATE) is also memory

mapped.Useful for read-modify-write operations on the value driven by the I/O pins.

I/O Bit Manipulation Programming

Single Bit Instructions for PIC18

BSF (bit set fileReg) BCF (bit clear fileReg)

BSF fileReg, bit_num

- to set HIGH a single bit of a given fileReg.

BCF fileReg, bit_num

- to clear a single bit of a given fileReg.

Example:

BSF PORTD,2 ;Set bit RD2

BCF PORTD,5 ;Clear bit RD5

EXAMPLE

An LED is connected to each pin of Port D. Write a program to turn ON each LED from pin D0 to pin D7.Call a delay module before turning ON the next LED.

Answer

BTFSS (bit test fileReg, skip if set) BTFSC (bit test fileReg, skip if clear)

EXAMPLE

EXAMPLE

EXAMPLE