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11 years, 4 months ago.
RS-232 8 byte word
I need to receive an 8 byte word that has 4 different functions. How do I break down or interpret the received word and assign the function to a GPIO (Out 0/1)
Function 1 : F9 FF FF FF FF A1 C2 00
Function 2: F9 FF BF FF FF A1 42 00
Function 3: F9 FF 7F FF FF A1 C2 00
Function 4: F9 FF E8 99 DF A1 66 00
Receiving function 2-4 will turn on a respective relay Receiving function 1 will turn off all relays
Baud Rate is 2400 one stop bit, no parity
I can read the data in but need to interpret bytes 3-7 for the functions
Any help is greatly appreciated
3 Answers
11 years, 4 months ago.
Have you written some sort of program yet?
Try buffering them, and then lookup in the buffer afterwards:
char buffer[8];
char function1[] = {F9, FF, FF, FF, FF, A1, C2, 00}; // Array for function
char function2[] = {F9, FF, BF, FF, FF, A1, 42, 00};
char function3[] = {F9, FF, 7F, FF, FF, A1, C2, 00};
char function4[] = {F9, FF, E8, 99, DF, A1, 66, 00};
Serial serial(p9, p10);
void serial_interrupt(){
if(serial.readable()){ // check availability
buffer[i] = serial.getc(); // copy the serial input to buffer
i++; // increment buffer value
}
}
int main() {
int i = 0;
serial.attach(&serial_interrupt(), Serial::RxIrq);
while(true){
if(!memcmp(buffer, function1, 8)){
// do stuff in here.
i = 0; // doing this prevents buffer overflow, i.e. you reset i, to point to buffer[0] again.
}
if(buffer == ....)
// And so on, you get the idea.
}
}
11 years, 4 months ago.
One addition:
Obviously all "packets" start with 0xf9. It would be a good idea to check incoming data in serial_interrupt() for this byte to be the first, and reset i on match. Christians Code would work well if the first incoming byte is guaranteed to be 0xf9, otherwise the buffer will never hold a proper packet, the memcmp will never match and i will never be reset, causing buffer to overflow.
Thus:
unsigned char d;
if(serial.readable()){ // check availability
d = serial.getc()
if (d == 0xf9) {
buffer[0] = d;
i = 1;
} else {
buffer[i] = d; // copy the serial input to buffer
i++; // increment buffer value
}
}
If it is not your only intention to do that job, it might be a good idea to place the memcmp within interrupt, checking when i becomes 7 and always resetting i in that case, so it will never overflow.
11 years, 4 months ago.
Christian and Rainer
First off than you for helping me here. I'm not a programmer by trade so please forgive my naiveté. With the code you have provided I keep getting an "identifier "i" is not identified" on the compile
The following communicates fine as a start, meaning reads proper data.
- include "mbed.h"
Serial pc(USBTX, USBRX); Serial uart(p9, p10); Connect TX to RX (p9 to p10) or can also use USB and type back in the number printed out in a terminal window
DigitalOut uart_activity(LED1); DigitalOut led2(LED2); DigitalOut led3(LED3); DigitalOut led4(LED4); assign led function
int main() { uart.baud(2400); while(1) { if(pc.readable()) { uart.putc(pc.getc()); pc_activity = !pc_activity } uart_activity = 0; turn off rx led if(uart.readable()) { pc.putc(uart.getc()); uart_activity = !uart_activity; wait(0.01); Turn on LED 1 when data recieved void Tx_interrupt(); void Rx_interrupt(); void send_line(); void read_line();
Circular buffers for serial TX and RX data - used by interrupt routines const int buffer_size = 255; might need to increase buffer size for high baud rates char tx_buffer[buffer_size]; char rx_buffer[buffer_size];
} } }
What follows is giving me the problems. The data is garbled, like a baud rate error, and I keep getting errors. What am I trying to do? Receive the commands via RS-232 then turn a set of GPIO functions on/off. In the program I was hoping to print the command on Cool Term and illuminate an LED when the functions occur. The GPIOs will be driving relays which in turn power a 3 axis motor system.
- include "mbed.h"
Serial pc(USBTX, USBRX); Serial uart(p9, p10); Connect TX to RX (p9 to p10) or can also use USB and type back in the number printed out in a terminal window
DigitalOut uart_activity(LED1); DigitalOut led2(LED2); DigitalOut led3(LED3); DigitalOut led4(LED4); assign led function
int main() { uart.baud(2400); while(1) { if(pc.readable()) { uart.putc(pc.getc()); pc_activity = !pc_activity } uart_activity = 0; turn off rx led if(uart.readable()) { pc.putc(uart.getc()); uart_activity = !uart_activity; wait(0.01); Turn on LED 1 when data recieved void Tx_interrupt(); void Rx_interrupt(); void send_line(); void read_line();
Circular buffers for serial TX and RX data - used by interrupt routines const int buffer_size = 255; might need to increase buffer size for high baud rates char tx_buffer[buffer_size]; char rx_buffer[buffer_size];
} } }
Any help would be welcome , thanks Thom