Omron CQM1H - PROGRAM Programming Manual page 470

Programmable controllers; inner boards

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Command and Response Formats

One word of data

Data from the same word is not divided.

FCS (Frame Check

Precautions for Long Transmissions

When dividing commands such as WR, WL, WC, or WD that execute write

operations, be careful not to divide into separate frames data that is to be writ-

ten into a single word. As shown in the illustration below, be sure to divide

frames so that they coincide with the divisions between words.

When a frame is transmitted, an FCS is placed just before the delimiter or ter-

minator in order to check whether any data error has been generated. The

FCS is 8-bit data converted into two ASCII characters. The 8-bit data is the

result of an EXCLUSIVE OR performed on the data from the beginning of the

frame until the end of the text in that frame (i.e., just before the FCS). Calcu-

lating the FCS each time a frame is received and checking the result against

the FCS that is included in the frame makes it possible to check for data

errors in the frame.

Node No. Header code

One word of data

Data from the same word is not divided.

FCS calculation range

Converted to hexadecimal.

Handled as ASCII characters.

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