Use Msp430 serial port interrupt to receive a packet of data-EEWORLD

Collect

Assume there is a data packet, the data format is as shown in the table:

Serial number	project	Length (bytes)	illustrate
1	Packet header (STX)	1	Constant: 0x02
2	Data unit length (Data_len)	2	The length of the Data part of the data unit to be transmitted, with the high byte in front and the low byte in the back. For example: 0x0010 means the Data part has 16 bytes.
3	Data unit to be transmitted (Data)	indefinite	The length is indicated by Data_len. The first two bytes of the data unit are the command code (the terminal sends a command to the reader) or the status code (the reader returns data to the terminal), followed by other parameters.
4	Redundancy Check Value (LRC)	1	The XOR value of each byte of the data in the Data part.
5	Packet tail (ETX)	1	Constant: 0x03

The total length of the data packet is: Data_len + 5 bytes, and the maximum length cannot exceed 512 bytes.

The program implementation is as follows:

[cpp] view plain copy print ?

#include
typedef struct newStruct
{
unsigned char startFlag;
unsigned char finishFlag;
unsigned char lenHighFlag;
unsigned char lenLowFlag;
unsigned char dataFlag;
unsigned char lrcFlag;
unsigned char buf[512];
unsigned char lenHigh;
unsigned char lenLow;
unsigned char dataStartIndex;
unsigned short len;
unsigned short index;
unsigned short tempLen;
}rxstruct;
rxstruct rxArray;
void m430_InitUart()
{
P3SEL |= BIT4|BIT5; // P3.4, P3.5 = USCI_A0 TXD/RXD
UCA0CTL1 |= UCSSEL_2; // SMCLK
//The following three lines are used to set the baud rate
UCA0BR1 = 0;
UCA0BR0 = 104; // 12MHz:1250->9600,625->19200,312->38400,214->56000,104->115200
UCA0MCTL = 0x02; // Modulation UCBRSx = 1
UCA0CTL1 &= ~UCSWRST; // Initialize USCI state machine
//IE2 |= UCA0RXIE | UCA0TXIE; //Note that the interrupt enable should be set after initializing USCI, otherwise it will not work. That is, if this sentence is placed before UCA0CTL1 &= ~UCSWRST;, the interrupt will not be responded to.
IE2 |= UCA0RXIE;
}
unsigned char uart_CalLrc(unsigned char *buf, unsigned short len)
{
unsigned short i;
unsigned char lrc;
lrc = 0x00;
for( i=0; i
{
lrc ^= buf[i];
}
return lrc;
}
void main()
{
WDTCTL = WDTPW + WDTHOLD;
BCSCTL1 = CALBC1_12MHZ;
DCOCTL = CALDCO_12MHZ;
m430_InitUart();
rxArray.startFlag = 0;
rxArray.finishFlag = 0;
_EINT();
_BIS_SR(LPM4_bits);
while(1)
{
}
}
#pragma vector = USCIAB0RX_VECTOR
__interrupt void uartRxHandle()
{
unsigned char num;
num = UCA0RXBUF;
if( 0==rxArray.startFlag )//Judge whether the frame header is received
{
if( 0x02==num )//Judge whether the frame header is correct
{
rxArray.startFlag = 1; //Sign that the frame header has been received
rxArray.finishFlag = 0;
rxArray.lenHighFlag = 0;
rxArray.lenLowFlag = 0;
rxArray.dataFlag = 0;
rxArray.lrcFlag = 0;
rxArray.index = 0;
rxArray.len = 0; //Storage frame length
rxArray.buf[rxArray.index] = num;
rxArray.index++;
}
return;
}
if( 0==rxArray.lenHighFlag )//Judge whether the high byte information of the frame length is received
{
rxArray.lenHighFlag = 1; // Flag that the high byte of the frame length has been received
rxArray.lenHigh = rxArray.buf[rxArray.index] = num;
rxArray.index++;
return;
}
if( 0==rxArray.lenLowFlag )//Judge whether the low byte information of the frame length is received
{
rxArray.lenLowFlag = 1; // Flag that the low byte of the frame length has been received
rxArray.lenLow = rxArray.buf[rxArray.index] = num;
rxArray.index++;
rxArray.dataStartIndex = rxArray.index;
rxArray.tempLen = rxArray.len = (rxArray.lenHigh<<8) + rxArray.lenLow; //Add one byte to the end of the frame
if( rxArray.len+5>512 )//If the data length is greater than 12, it means that the received data length information is incorrect and needs to be received again
{
rxArray.startFlag = 0;
rxArray.lenHighFlag = 0;
rxArray.lenLowFlag = 0;
}
return;
}
if( 0==rxArray.dataFlag )
{
rxArray.buf[rxArray.index] = num; //Store the data in the array
rxArray.index++;
rxArray.tempLen--;
if( 0==rxArray.tempLen )
{
rxArray.dataFlag = 1;
}
return;
}
if( 0==rxArray.lrcFlag )//Receive lrc
{
rxArray.buf[rxArray.index] = num;
rxArray.index++;
rxArray.lrcFlag = 1;
if( 0!=uart_CalLrc( &rxArray.buf[rxArray.dataStartIndex], rxArray.len+1 ) )//Judge whether the lrc of the received data is correct
{
rxArray.startFlag = 0;
rxArray.lenHighFlag = 0;
rxArray.lenLowFlag = 0;
rxArray.dataFlag = 0;
rxArray.lrcFlag = 0;
}
return;
}
rxArray.buf[rxArray.index] = num;
rxArray.finishFlag = 1;
rxArray.startFlag = 0;
rxArray.lenHighFlag = 0;
rxArray.lenLowFlag = 0;
rxArray.dataFlag = 0;
rxArray.lrcFlag = 0;
if( rxArray.buf[rxArray.index]!=0x03 )//The last byte is not 0x03, indicating that the data is incorrect and needs to be received again
{
rxArray.finishFlag = 0;
}
if( rxArray.finishFlag )
{
//Received data processing part
}
}

A fatal bug in this program is that if an error occurs when receiving the two bytes of length information, a packet of data cannot be correctly formed, and subsequent data packets cannot be received correctly.

For example, there is a packet of data (hexadecimal): 02 00 02 11 11 00 03,

If an error occurs during the receiving process, the two bytes of length 00 02 will be changed to 00 05 at the receiving end. Therefore, the receiving end will wait until 5 bytes of data are received before considering that a packet of data has been completely received. As a result, part of the complete data packet sent later will be split. This vicious cycle will continue over and over again, and no good solution has been found yet!

Keywords：Msp430 Reference address：Use Msp430 serial port interrupt to receive a packet of data

Previous article：MSP430F2131 reads and writes DS1991
Next article：Which interfaces can be used to program MSP430?

Popular Resources
Popular amplifiers