This post provides the software UART (Bit Banging) code for PIC12F675 microcontroller (e-g to connect PIC controller with PC using serial adapter).
As we know, PIC12F675 microcontroller doesn’t have built in UART module, so we can create UART functionality in it’s software. This post provides the details of how to program software UART functionality in PIC12F675. This code is written in C language using MPLAB with HI-TECH C compiler. You can download this code from the ‘Downloads‘ section at the bottom of this page.
It is assumed that you know how to blink an LED with PIC12F675 microcontroller. If you don’t then please read this page first, before proceeding with this article.
The result of simulating the code in Proteus is shown below.
In the above figure, PIC12F675 is running at 4MHz internal crystal. GP0 pin is being used as TX pin and GP1 pin is the RX pin of the software UART.
The code used to set different properties of UART is shown below. (From Software_UART.h file)
In the above figure, _XTAL_FREQ is defined to be 4000000, which is the internal crystal frequency used with this PIC12F675. If you change the crystal (e-g by attaching an external crystal of different frequency) then you will need to change _XTAL_FREQ value as well. For example, if 20MHz external crystal is used, then _XTAL_FREQ should be defined as 20000000 in the above code.
Similarly, you can define Baudrate for the UART, in the above figure it is defined to be 1200 bps. Since this is a software UART, that is why when you increase Baudrate , then bit error rate for UART also increases drastically. You should increase crystal value to reduce UART bit errors. For example to use a Baudrate of 4800, you should use a crystal of atleast 20MHz. DataBitCount is defined to be 8, which means this UART will use one starting bit, 8 data bits and then one stop bit. There is no parity bit and no flow control mechanism.
Software UART code for PIC12F675 was compiled in MPLAB v8.85 with HI-TECH C v9.83 compiler and simulation was made in Proteus v7.10. To download code and Proteus simulation click here.
For more detail: PIC12F675 software UART (bit banging) code and Proteus simulation