B&B Electronics MODSCAN32 - Manual - Manual (Page 75)

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Modbus Data Control Description
The Modbus Data Control, (modbuss), reflects the status of one or more I/O data points contained within a
connected MODBUS slave device. Each control contains an array of up to 128 boolean values, (Coils),
128 integer values, (Registers), or 64 Floating Point values. The data is defined by properties which
identify the device and point address. Standard OLE Get and Set methods allow modbus data points to be
accessed transparently by the controlling application by simply moving data to/from the array.
Properties
The following properties and methods define the operating characteristics of the Modbus Data Control:
Port
The PC COM port identification. (May be overridden by the UseNetwork
property.)
Node MODBUS slave device address.
Address Defines the starting data point address within the designated slave device.
The address specification implicitly defines the MODBUS message type used
to access the data.
Address Range
Function Code Data Type
00001-09999
01 Coil Status
10001-19999 02 Input Status
30001-39999 04 Input Registers
40001-49999 03 Holding Registers
Length Defines the number of data points to be scanned from the MODBUS slave
device. If floating point values are used, remember that each 32-bit floating-
point value requires two consecutively numbered 16-bit MODBUS registers.
The Length property must be defined in either the number of Coils or the
number of Registers scanned from the device. For example, if a control is
configured to expect 40 floating point values, the Length property would be
set to 80. The maximum number of values which may be scanned from any
particular MODBUS slave device may be less than 128. If a control is
configured to scan more values than the device can support, an exception
status will be generated by the control.
Busy Indicates that control is processing a modbus message to a connected slave.
The Busy property is set by the control whenever a poll for data is made to
the MODBUS slave. It is cleared when the requested data is received or the
when the device times-out. The Busy property may be used by the
application to synchronize data requests. If an Update request is made with
the Busy flag set, the control will ignore the request and return an error
condition, (FALSE). The only exception to this is in the event a Poll for data
takes longer than 10 seconds, in which case the Update() Method overrides
the Busy indication and initiates a new poll.
Status This status property is set by the control to indicate an error condition. This