ProSoft Technology MVI94-MCM-MHI - Manual (Page 84)

Reference MVI94-MCM ♦ Flex I/O Platform
User Manual Serial Communications Modbus Communication Module
Page 84 of 109 ProSoft Technology, Inc.
March 29, 2011
5.4.2 Read Coil Status (Function Code 01)
Query
This function allows the user to obtain the ON/OFF status of logic coils used to
control discrete outputs from the addressed Slave only. Broadcast mode is not
supported with this function code. In addition to the Slave address and function
fields, the message requires that the information field contain the initial coil
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 coils to be obtained at each request; however,
the specific Slave device may have restrictions that lower the maximum quantity.
The coils are numbered from zero; (coil number 1 = zero, coil number 2 = one,
coil number 3 = two, and so on).
The following table is a sample read output status request to read coils 0020 to
0056 from Slave device number 11.
Adr Func Data Start Pt Hi Data Start Pt Lo Data # Of Pts Ho Data # Of Pts Lo Error Check Field
11 01 00 13 00 25 CRC