File content as of revision 0:bcd01ae054eb:

#include "mbed.h"
#include "crc.h"

Serial pc(SERIAL_TX, SERIAL_RX);

Serial uart(PA_11, PA_12);
DigitalOut RTS(D12);

DigitalOut dbg(D2);
DigitalOut flip(D3);

volatile int rx_count = 0;
uint8_t rx_buffer[100];

void rxCallback() {
    while (uart.readable()) {
        rx_buffer[rx_count] = uart.getc();
        rx_count++;
    }
}

void write_get_position(uint8_t id) {
    uint8_t tx_buffer[14];
    rx_count = 0;    

    tx_buffer[0] = 0xff;
    tx_buffer[1] = 0xff;
    tx_buffer[2] = 0xfd;
    tx_buffer[3] = 0x00;
    tx_buffer[4] = id; //ID
    tx_buffer[5] = 0x07; //length
    tx_buffer[6] = 0x00; //length2
    tx_buffer[7] = 0x02; //read command
    tx_buffer[8] = 0x84; //position identifier
    tx_buffer[9] = 0x00;
    tx_buffer[10] = 0x04; 
    tx_buffer[11] = 0x00; 
    uint16_t crc = update_crc(0, tx_buffer, 12);
    tx_buffer[12] = crc & 0xff;
    tx_buffer[13] = (crc >> 8) & 0xff;
    
    printf("0x%x 0x%x\n", tx_buffer[12], tx_buffer[13]);
    
    RTS = 1;
    wait_us(100);
    for (int i = 0; i < 14; i++) {
        uart.putc(tx_buffer[i]);
    }
    wait_us(200);
    RTS = 0;
    
    flip = 1;
    while (rx_count < 15) {
    }
    flip = 0;
    
    for (int i = 0; i < 15; i++) {
        pc.printf("0x%x ", rx_buffer[i]);
    }
    pc.printf("\n");
}

int main()
{
    pc.baud(115200);
    uart.baud(115200);
    uart.attach(rxCallback);
    
    pc.printf("Program is running!\n");
    
    for (;;) {
        dbg = 1;
        write_get_position(0x01);
        dbg = 0;
        wait(1);
    }
}