Structure of Frame

Owned by CIMON (Unlicensed)
Mar 21, 2024
1 min read

Request Frame (Master) :

The frame that an outside communication device requests to a computer link module

 

ENQ

Stn

H

Stn

L

Cmd

Leng

H

Leng

L

Data

BCC

H

BCC

L

EOT

 

 

 

Response Frame (Slave) :

The frame that a computer link module responds to an outside communication device

 

STX

Stn

H

Stn

L

Cmd

Leng

H

Leng

L

Data

BCC

H

BCC

L

ETX

 

  • The structure of a sending frame and the one of a receiving frame are same.

  • The same as the command codes received from a request frame (Master) are used for response frame. But, if there is an error in communication or process, Code E is responded.

  • Description for Codes

 

Code

Hex Value

Description

ENQ

05H

Master Frame Header

EOT

04H

Master Frame Tail

STX

02H

Slave Header

ETX

03H

Slave Tail

Stn

00H~1FH, FFH

PLC Station Number

Cmd

 

Command

Leng

 

Length of Data Device (Length Bytes), Hexadecimal

Data

 

Data Device according to Command (Length Bytes)

BCC

 

Remainder value when dividing the binary-sum from Cmd to the end of data by 256

 

 Commands

The commands used for exclusive communication service are as follows.

Command

Code

ASCII

Function

Read Word Data

52H

R

Reads Word Memory Device.

Write Word Data

57H

W

Writes to Word Memory Device.

Read Bit Data

72H

r

Reads Bit Memory Device.

Write Bit Data

77H

w

Writes to Bit Memory Device.

Change PLC Mode

4DH

M

Changes PLC Mode.

Register Monitoring Device

58H

X

Registers Monitoring Device.

Read Monitoring Device

59H

Y

Reads Registered Monitoring Device

Respond Error

45H

E

Responds Error in PLC.