Serial Port Complete - Latest Microcontroller projects

Chapter 11

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To use the transmit and received interrupts without using interrupt priority:

1. In the PIE1 register, set TXIE = 1 and RCIE = 1.


2. In the INTCON register, set GIE = 1 and PIE = 1.
   To use the transmit and received interrupts with interrupt priority:


3. In the RCON register, set IPEN = 1.


4. In the PIE1 register, set TXIE = 1 and RCIE = 1.


5. In the IPR1 register, set the interrupt priority in RCIP and TXIP as desired.


6. In the INTCON register, set GIEH and GIEH to enable interrupts as appro-
   priate for the IPR1 settings.





To transmit a byte, firmware performs these tasks:

1. To enable transmitting, in the TXSTA register, set TXEN = 1.


2. If using hardware flow control, check the state of the firmware-defined
   flow-control input bit and wait as needed for permission to transmit.


3. Write a byte to transmit to TXREG. The byte transfers to the TSR. When
   TXREG is empty, in the PIR1 register, TXIF = 1. On the TX pin, the TSR
   transmits a Start bit, the byte of data, and a Stop bit.
   Firmware can write another byte to TXEN as soon as TXIF = 1. If using inter-
   rupts, firmware will jump to the ISR when TXIF = 1.

5 

To receive a byte, firmware performs these tasks:

1. To enable receiving, in the RCSTA register, set CREN = 1.


2. If using hardware flow control, set the firmware-defined flow-control output
   bit to enable receiving.


3. In the PIR1 register, wait for RCIF = 1, indicating the receive buffer contains
   as least one byte. If using interrupts, firmware will jump to the ISR when RCIF
   = 1.


4. In the RCSTA register, check the framing error (FERR) and overrun
   (OERR) bits.


5. Read the received byte in RCREG. Reading the register clears RCIF. If FERR
   = 1, firmware will likely want to discard the received byte.