Switching UART on and off

[robin171]

Hello,

I have a problem with the #use UART statement

I have a ST7538 powerline transceiver connected to a PIC16F877A. RX and TX of the transceiver are connected to the hardware UART of the 16f887a. The CLR/T pin is connected to the B0 / INT pin of the microcontroller.

The ST7538 uses the CLR/T as a clock output for synchronous communication with a microcontroller. If you want to write the control register of the powerline transceiver, you must use synchronous communication.

I wrote a interrupt function for EXT_INT that writes 24 bits to the powerline tranceiver via pin C6. I tested this function with the scope, it works fine until I declare the following statement:

[RLScott]

The block diagram in figure 12-1 of the datasheet shows SPEN controlling the hardware UART's use of the TX pin (RC6). You can assume when your main program starts that the CCS runtime code has already initialized everything, including the RCSTA register that has the SPEN bit. So you need to override that by temporarily clearing RCSTA.SPEN until you have done your custom thing with RC6, and then set SPEN back to 1 when you want to enable the hardware serial port.

You can get direct access to the RCSTA register by declaring:

[ckielstra]

As an alternative to directly accessing the SPEN bit you can use the setup_uart function which does the same thing but is easier to read.