Mitsubishi MELSEC Q Series Reference Manual page 314

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3 WHEN COMMUNICATING USING THE QnA COMPATIBLE 3E/3C/4C FRAMES OR 4E FRAME
(b) When the "Word/byte units designation" in GX Works2 or GX Configurator-
SC is set to "1" (byte units)
The following diagram shows the control procedure when two words (four
bytes) are designated as transmission data.
POINT
(1) The number of bytes in the transmission data section of the on-demand data
is the same as the data length.
(One byte is used for one byte of data.)
(2) When the data length is an odd number, the data of the lower byte (bits 0 to 7)
of the last data storage device is transmitted.
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