bit_bang_uart.c File Reference

bit-bang UART implementation More...

#include "bit_bang_uart.h"
#include "msp430x24x.h"

Defines
#define	MDB   1
#define	BIT_BANG_TX_PORT   P6OUT
#define	BIT_BANG_TX_BIT   BIT7
#define	BIT_BANG_RX_PORT   P2IN
#define	BIT_BANG_RX_BIT   BIT5
#define	DISABLE_BIT_BANG_RX_INTERRUPT()   (P2IE &= ~BIT5)
#define	ENABLE_BIT_BANG_RX_INTERRUPT()   (P2IE |= BIT5)
#define	BIT_LENGTH_9600   160
#define	HALF_BIT_LENGTH_9600   76
#define	BIT_LENGTH_19200   75
#define	HALF_BIT_LENGTH_19200   27
#define	OUTPUT_1()   (BIT_BANG_TX_PORT |= BIT_BANG_TX_BIT)
#define	OUTPUT_0()   (BIT_BANG_TX_PORT &= ~BIT_BANG_TX_BIT)
#define	NUMBER_OF_DATA_BITS   8
#define	TOGGLE_DEBUG_PIN()   (P4OUT ^= BIT5)
Functions
void	delayFullBit ()
void	delayHalfBit ()
void	bitBangOutput (unsigned char outputByte)
char	bitBangInput ()

---

Detailed Description

bit-bang UART implementation

This file implements a simple software defined Universal Asynchronous Receiver/Transmitter (UART). For simplicity and portability, timing is done using delay loops. Depending on hardware resources, you may want to use a timer instead.

Baud rate is 19200 in the format 8-N-1: 8 data bits, no parity, 1 stop bit. Line is normally high.

The defines will need to be modified if changing hardware implementation.

Note:

if changing hardware implementation, first verify with an oscilloscope or similar that the timing is correct. For example, bit width in 9600 bps one bit width is 104.2uSec, at 19,200 it is 52.08uSec, and at 38,400 it is 26.041uSec. Best way to do this is output 'U' and measure the bit widths.

Rev

365

Author

dsmith

Date

2010-03-24 16:57:31 -0700 (Wed, 24 Mar 2010)

URL

http://dsmith@ns.svnrepository.com/svn/hardware/fw/ZNP%20Examples/bit_bang_uart.c

---

Function Documentation

char bitBangInput

(

)

Blocking UART receiver. Called by BIT_BANG_RX_PORT Interrupt Service Routine upon detection of start bit (high to low transition). BIT_BANG_RX_BIT should be configured as high-low edge triggered interrupt. Receives a byte and then processes it.

Note:

BIT_BANG_RX_PORT, BIT_BANG_RX_BIT, DISABLE_BIT_BANG_RX_INTERRUPT(), and ENABLE_BIT_BANG_RX_INTERRUPT() must be defined. Modify accordingly for other hardware.

Precondition:

Oscillator configured for 8MHz

A high-to-low transition has occurred on BIT_BANG_RX_BIT

Returns:

the byte received

void bitBangOutput

(

unsigned char

outputByte

)

Transmits one byte out the specified pin

To Send a Byte

• Line is nominally at '1' (high)
• 1 Start bit = '0'
• Data, MSB first, LSB last. '1' = line high, '0' = line low
• 1 Stop bit = '1' (idle, or high)

  Note:

  BIT_BANG_RX_PORT, BIT_BANG_RX_BIT, DISABLE_BIT_BANG_RX_INTERRUPT(), and ENABLE_BIT_BANG_RX_INTERRUPT() must be defined. Modify accordingly for other hardware.

  Precondition:

  Oscillator configured for 8MHz

  port/bit configured for logic output.

  bit is high (logic '1')

  Parameters:

  byte

  the byte to output

void delayFullBit

(

)

Simple delay for bit width. Used in transmit and receive.

void delayHalfBit

(

)

Simple delay for 1/2 of bit width. Used in receive.