B–18

Communications Reference Information

Block CheckCode (BCC)

Appendix B

This section shows how the inverter protocol computes defines a BCC—block check code. The BCC is calculated for each frame transmitted and can be used to verify the integrity of data transmission. The example below shows command 01 setting the inverter frequency to 5Hz.

Frame format

STX Node Command Data BCC [CR]

 

 

 

 

 

 

 

ASCII Code

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(0x

02)

 

 

 

 

 

 

 

 

 

 

 

 

 

0 1

(0x

30 31)

 

 

 

 

 

 

 

 

 

 

 

0 1

(0x

30 31)

 

 

 

 

 

 

 

 

 

 

0 0 0 5 0 0

(0x

30 30 30 35 30 30)

 

 

 

 

 

 

 

 

 

0

(0x

30 35)

 

 

 

 

 

 

 

 

 

(0x

0D)

 

 

 

 

 

 

 

The block check code is computed by using the ASCII codes (shown above) and applying eXclusive OR (XOR) operations. Beginning with the first pair of bytes, the result of their XOR result is then used in an XOR operation with the third byte, and so on. For this example, the BCC calculation is shown below.

Data bytes:

 

 

 

 

 

 

 

 

3 0

3 1

3 0

3 1

3 0

3 0

3 0

3 5

3 0

3 0

0 1

3 1

 

 

 

 

 

XOR

0 0

 

 

 

 

 

intermediate results

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3 0

 

 

 

 

 

 

0 0

3 0

0 5

3 5

0 5 BCC

ASCII Code Table The table below shows only the ASCII codes used for function codes and parameter data.

 

CharacterASCII Code

Character

ASCII Code

Character

ASCII Code

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

STX

0 2

4

3 4

C

4 3

 

 

 

 

 

 

 

 

 

 

ACK

0 6

5

3 5

D

4 4

 

 

 

 

 

 

 

 

 

 

CR

0 D

6

3 6

E

4 5

 

 

 

 

 

 

 

 

 

 

NAK

1 5

7

3 7

F

4 6

 

 

 

 

 

 

 

 

 

 

0

3 0

8

38

H

4 8

 

 

 

 

 

 

 

 

 

 

1

3 1

9

39

P

5 0

 

 

 

 

 

 

 

 

 

 

2

3 2

A

4 1

—

—

 

 

 

 

 

 

 

 

 

 

3

3 3

B

4 2

—

—