Rockwell-automation 1775-KA PLC-3 Communication Adapter Module User Ma Manual de usuario descargar pdf (Pagina 109)

Full-Duplex Protocol

Chapter 10

105

Block Check

The block check character (BCC) is a means of checking the accuracy of

each message packet transmission. It is the 2’s complement of the 8–bit

sum (modulo–256 arithmetic sum) of all data bytes between the DLE

STX and the DLE ETX BCC. It does not include any other message

packet codes or response codes.

For example,if message packet contained the data codes 8, 9, 6, 0, 2, 4,

and 3, the message packet codes would be (in hex):

10 02 08 09 06 00 02 04 03 10 03 EO

DLE STX Data DLE ETX BCC

The sum of the data bytes in this message packet is 20 hex. The BCC is the 2's

complement of this sum, or EO hex. This is shown in the following binary

calculation:

0010 0000 20 hex

11011011 1s compliment

1110 0000 2s compliment (E0 hex)

To transmit the data value 10 hex, you must use the data code DLE DLE.

However, only one of these DLE data bytes is included in the BCC sum.

For example, to transmit the values 8, 9, 6, 0, 10, 4, and 3 hex, you would

use the following message codes:

Represents single data byte value of 10

10 02 08 09 06 00 10 10 04 03 10 03 D2

DLE STX Data DLE ETX BCC

In this case, the sum of the data bytes is 2E hex because only one DLE

text code is included in the BCC. So the BCC is D2 hex.

1 2 ... 104 105 106 107 108 109 110 111 112 113 114 ... 238 239

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Rockwell-automation 1775-KA PLC-3 Communication Adapter Module User Ma Manual de usuario Pagina 109