MBS Protocol PLX3x Series
User Manual Ethernet and Serial Gateways
Page 140 of 218 ProSoft Technology, Inc.
May 26, 2016
Because the server interface device is serviced at the end of a controller's scan,
data will reflect coil status at the end of the scan. Some servers will limit the
quantity of coils provided each scan; thus, for large coil quantities, multiple PC
transactions must be made using coil status from sequential scans.
Data Coil
Status 20 to
27
Data Coil
Status 28 to
35
Data Coil
Status 36 to
43
Data Coil
Status 44 to
51
Data Coil
Status 52 to
56
The status of coils 20 to 27 is shown as CD (HEX) = 1100 1101 (Binary).
Reading left to right, this shows that coils 27, 26, 23, 22, and 20 are all on. The
other coil data bytes are decoded similarly. Due to the quantity of coil statuses
requested, the last data field, which is shown 1B (HEX) = 0001 1011 (Binary),
contains the status of only 5 coils (52 to 56) instead of 8 coils. The 3 left most bits
are provided as zeros to fill the 8-bit format.
Read Input Status (Function Code 02)
Query
This function allows the user to obtain the ON/OFF status of discrete inputs in the
addressed server PC Broadcast mode is not supported with this function code. In
addition to the server address and function fields, the message requires that the
information field contain the initial input address to be read (Starting Address)
and the number of locations that will be interrogated to obtain status data.
The addressing allows up to 2000 inputs to be obtained at each request;
however, the specific server device may have restrictions that lower the
maximum quantity. The inputs are numbered form zero; (input 10001 = zero,
input 10002 = one, input 10003 = two, and so on, for a 584).
The following table is a sample read input status request to read inputs 10197 to
10218 from server number 11.
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