Really Soft UART

[paulpthcom 19]

So I'll start up by admitting this is horrible code, you probably shouldn't use it and it's just generally a bad idea, but someone might find it useful. I'm targeting a 2452 without hardware UART and wanted to be able to printf solely for debugging purposes. I know that there's at least one implementation that uses Timer A and T0.1 to implement a soft UART. That version is much more bullet proof and if you actually need to get every last byte you should use that, or better yet a chip with a hardware UART.

 

That being said I only need this for debugging and can miss a character once in a while in exchange for being able to use any pin and having simpler interrupt logic. It's just a simple pure bit bang implementation but I wasn't able to find anything like it out there. Seems to work rather well at 57600 with only a junk character once in a great while. Anyways enjoy or laugh at, you won't hurt my feelings either way.

 

//#define BIT_DELAY __delay_cycles((1000000/9600) - 12) // 9600 BAUD

#define BIT_DELAY ; // 57600 BAUD


unsigned char *g_port_out;

unsigned char g_port_bit;


void uart_init(unsigned char *port_out, unsigned char *port_dir, unsigned char port_bit)

{

g_port_out = port_out;

g_port_bit = port_bit;


*port_dir |= port_bit;

*g_port_out |= port_bit;

BIT_DELAY;


// Clear screen

printf("\033[2J\033[0;0f");

printf("\033[%d;%df", 0, 0);

}


int putchar(int c)

{

unsigned int tx_byte = (c | 0x100) << 1; // Add HIGH stop bit and low start bit


while (tx_byte) {

if (tx_byte & 0x1) {

*g_port_out |= g_port_bit;

} else {

*g_port_out &= ~g_port_bit;

}

tx_byte = tx_byte >> 1;


BIT_DELAY;

}


*g_port_out |= g_port_bit;


if (c == '\n')

putchar('\r');


return 1;

}

[Rei Vilo 695]

I've developed a Very Basic Software Serial TX Only Library

 

By very basic, I mean TX only, one single speed 9600 and one single configuration is 8N1.

 

The library uses the Energia framework but shouldn't be difficult to adapt to another environment. 

[lalalandrus 16]

the timer way is probably the way to go, but if you are short on timers, you can always use the WDT in interval mode...