PLX30 Series
MBS Protocol
Ethernet and Serial Gateways
User Manual
ProSoft Technology, Inc.
Page 145 of 200
September 19, 2012
Response
The addressed server responds with its address and the function code followed
by the information field. The information field contains 1 byte describing the
quantity of data bytes to be returned. The contents of the registers requested
(DATA) are 2 bytes each, with the binary content right justified within each pair of
characters. The first byte includes the high order bits and the second, the low
order bits.
Because the server interface is normally serviced at the end of the controller's
scan, the data will reflect the register content at the end of the scan. Each PC will
limit the quantity of register contents provided each scan; thus for large register
quantities, multiple PC scans will be required, and the data provided will be form
sequential scans.
In the example below the register 3009 contains the decimal value 0.
Adr
Func
Byte Count
Data Input Reg Hi
Data Input Reg Lo
Error Check Field
11
04
02
00
00
E9
Force Single Coil (Function Code 05)
Query
This message forces a single coil either ON or OFF. Any coil that exists within
the controller can be forced to either state (ON or OFF). However, because the
controller is actively scanning, unless the coil is disabled, the controller can also
alter the state of the coil. Coils are numbered from zero (coil 0001 = zero, coil
0002 = one, and so on). The data value 65,280 (FF00 HEX) will set the coil ON
and the value zero will turn it OFF; all other values are illegal and will not affect
that coil.
The use of server address 00 (Broadcast Mode) will force all attached servers to
modify the desired coil.
Note:
Functions 5, 6, 15, and 16 are the only messages that will be recognized as valid for
broadcast.
The example below is a request to server number 11 to turn ON coil 0173.
Adr
Func
Data Coil # Hi
Data Coil # Lo
Data On/off Ind
Data
Error Check Field
11
05
00
AC
FF
00
CRC
