Logging data to SD card from software serial
use the C as the line start indicator. if received char is 'C' then do a file.println(); example with output to Serial

#include &lt;SoftwareSerial.h&gt; 
SoftwareSerial mySerial(8,9); 

void setup() {
    Serial.begin(9600);
    mySerial.begin(9600);
    mySerial.print("C");
}

void loop() {
 if (mySerial.available()) {
   char c = mySerial.read();
   if (c == 'C') {
     Serial.println();
   }
   Serial.write(c);
 }
}