PORTx - Data Register

PORTx is a bidirectional port, and its corresponding data direction register is TRISx.

Reading the PORTx register reads the status of the pins, whereas writing to it will write to the PORT latch. All write operations are Read-Modify-Write operations. Therefore, a write to a port implies that the PORT pins are read, and this value is modified, then written to the PORT data latch (LATx). The PORT data latch LATx holds the output port data and contains the latest value of a LATx or PORTx write. The example below shows how to initialize PORTA.

Initializing PORTA in Assembly


; This code example illustrates initializing the PORTA register. 
; The other ports are initialized in the same manner.

    BANKSEL    PORTA        ;
    CLRF       PORTA        ;Clear PORTA
    BANKSEL    LATA         ;
    CLRF       LATA         ;Clear Data Latch
    BANKSEL    ANSELA       ;
    CLRF       ANSELA       ;Enable digital drivers
    BANKSEL    TRISA        ;
    MOVLW      B'00111000'  ;Set RA[5:3] as inputs
    MOVWF      TRISA        ;and set others as outputs

Initializing PORTA in C

// This code example illustrates initializing the PORTA register. 
// The other ports are initialized in the same manner.

    PORTA  = 0x00;       // Clear PORTA
    LATA   = 0x00;       // Clear Data Latch 
    ANSELA = 0x00;       // Enable digital drivers
    TRISA  = 0x38;       // Set RA[5:3] as inputs and set others as outputs
Important: Most PORT pins share functions with device peripherals, both analog and digital. In general, when a peripheral is enabled on a PORT pin, that pin cannot be used as a general purpose output; however, the pin can still be read.