Novatek UBZ-304 Operating Manual Download

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UBZ-304

NOVATEK-ELECTRO

Request

Address Function Sub-function HB

Sub-function LB

Data HB

Data LB CRC LB

CRC HB

01h

08h

00h

A0h

3Ch

98h

1Ah

Response

Address Function Sub-function HB

Sub-function LB

Data HB

Data LB CRC LB

CRC HB

01h

08h

00h

A0h

3Ch

98h

1Ah

Figure 5.13

–

Example of request and response for sub-function 00h

–

return of request data

Sub-function 01h

–

restart of communication options

During fulfillment of the command UBZ performs only change in baud rate. To change totally the communication

settings you should run the command "UBZ RESTART" ("RESTART").

Example of request and response for MODBUS

RTU

mode is shown in Fig.5.14.

Request

Address Function Sub-function HB

Sub-function LB

Data HB

Data LB CRC LB

CRC HB

01h

08h

00h

01h

00h

B1h

CBh

Response is not returned

Figure 5.14

–

Example of request and response for sub-function 01h

–

restart of communication options

5.4.5 Control of correct transmission of data packet

5.4.5.1 Control of correct transmission of data packet in

RTU

mode

To check the correctness of data transmission in

RTU

mode the CRC Cyclic Redundant Check

–

the code for

cyclic control is used.

The Cyclic Redundant Check (CRC16) is a cyclic verification code based on the polynomial A001h. The

transmitting device forms the Cyclic Redundant Check for all bytes of the message transmitted. The receiving
device similarly generates the Cyclic Redundant Check for all bytes of the message received and compares it with
the Cyclic Redundant Check received from the transmitting device. In case of mismatching the generated and
received Cyclic Redundant Check the error message will be generated.

The field of Cyclic Redundant Check has two bytes. CRC in the message is transferred with low byte first.
CRC is formed by the following algorithm:

1) loading CRC register (16 bit) by units (FFFFh);
2) exclusive OR with the first 8 bits of the byte of the message and CRC register contents;
3) shift of the result one bit to the right;
4) if shifted bit = 1, exclusive OR of the contents of the register with value A001h;
5) if shifted bit = 0, repeat step 3;
6) repeat steps 3, 4, 5, until 8 shifts;
7) exclusive OR with the following 8 bits byte of the message and CRC register contents;
8) repeat steps 3 to 7 until all bytes of the message will be processed;
9) the final contents of the register will contain the CRC.

Example of Program CRC code generation in the language C. the Function has two arguments:

Unsigned char* data <- a pointer to the message buffer
Unsigned char length <- the quantity of bytes in the message buffer
The function returns the CRC value as a type of unsigned integer.
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 & 0х01) reg_crc=(reg_crc>>1) ^ 0xA0

01; // LSB(b0)=1

          else reg_crc=reg_crc>>1;
     }
}
return reg_crc;
}

5.4.5.2

Control of correct transmission of data packet in ASCII mode

To check the correctness of data transfer in

ASCII

mode LRC Redundant Check

–

longitudinal redundancy

check. CRC is 8

–