Function

Calculate CRC16 (CRC-16-IBM, also known as CRC-16-ANSI)  x¹⁶ + x¹⁵ + x² + 1

Purpose

To verify data transmitted. Used at Bisync, Modbus, USB, ANSI X3.28, SIA DC - 07, and many others

Syntax

void updateCRC16(uns8 value)

Parameters

value: next data byte to update

Input values

Crc16  16b CRC value before update. The initial value (before the first byte is updated) must                 be specified (the same as at the counterpart).

Return value

  –

Output values

Crc16    Updated CRC value

Preconditions

 –

Remarks

 –

Side effects

 –

See also

 –

Example

  // Verifying data incoming via UART

bit RxUART();              // Returns TRUE when a byte (stored in variable                                 // RxUARTdata) from UART was successfully received

static uns8 RxUARTdata;   // Global variable holding the byte received by function                             // RxUART()

…

FSR1 = …;                  // FSR1 points to the message buffer

Crc16 = 0xFFFF;            // Initial CRC value (use the same value as the one used                             // at the transmitting counterpart)

uns8 msgLength = 0;       // Reset the message length

while (RxUART())           // Read the message from UART, store it, count the                             // message length and update CRC

{

  setINDF1(RxUARTdata);    // Store the byte received

  UpdateCrc16 (*FSR1++);  // Update CRC and increment the pointer     

  msgLength++;              // Update the message length   

}

if (Crc16 == 0)            // Is CRC valid?

  // Yes

  …