Delta DVP-SS2 User Manual

4. Communications
4-9
obtained in the CRC register is the CRC checksum. Care should be taken when placing the LOW byte
and HIGH byte of the obtained CRC checksum.
Calculation example of the CRC Check using the C language:
unsigned char* data  // index of the command message
unsigned char length  // length of the command message
unsigned int crc_chk(unsigned char* data, unsigned char length)
{
int j;
unsigned int reg_crc=0Xffff;
while(length--)
{
reg_crc ^= *data++;
for (j=0;j<8;j++)
{
If (reg_crc & 0x01) reg_crc=(reg_crc>>1) ^ 0Xa001; /* LSB(b0)=1 */
else reg_crc=reg_crc >>1;
}
}
return reg_crc; // the value that sent back to the CRC register finally
}
Exception response:
The PLC is expected to return a normal response after receiving command messages from the master
device. The following content depicts the conditions that either no response situation occurs or an error
response is replied to the master device.
1. The PLC did not receive a valid message due to a communication error; thus the PLC has no
response. In this case, condition of communication timeout has to be set up in the master device
2. The PLC receives a valid message without a communication error, but cannot accommodate it. In
this case, an exception response will return to the master device. In the exception response, the
most significant bit of the original command code is set to 1, and an exception code explaining the
condition that caused the exception is returned.

Delta DVP-SS2 Specifications

General

Brand	Delta
Model	DVP-SS2
Category	Controller
Language	English