User`s manual

Western Reserve Controls, Inc. 1782-JDC User’s Manual
3
Table 1-1 I/O Message Types
Typical Data Polled Cyclic Bit-Strobe Change-of-State Explicit Message
Commands
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Status
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Parameters
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The following sections describe how the data is accessed.
1.3.1 Polled I/O
The DeviceNet Master uses the JDC’s predefined polled IO connection to send input and output
data to the JDC. The input data to the JDC has a one byte record number and up to 125
additional bytes of transmit data. When a poll is received and the record has changed since the
last poll was sent, the JDC sends the associated transmit data out the serial port to the remote
ASCII device. When the JDC receives serial data from a device on the serial link, the poll
response data to the Master contains a one byte record number, then a one byte status number
that reflects errors or events on the bus and up to 126 bytes of received data. The record number
is incremented in the poll response when new data is received on the serial link. The status byte is
zero if no errors occurred.
1.3.2 Explicit Messages
As mentioned explicit messages are typically used to read and write configuration data. This data
allows the JDC to change its internal operating parameters such as baudrate and parity. The JDC
does not allow for direct communication to the serial ports using explicit messaging.
1.3.3 Cyclic Input Message (not currently implemented)
Cyclic I/O is the function by which a slave device sends its input data to the master at a specific
time period without the host explicitly requesting it. When the specified time interval (defined by
you) elapses, the user-specified input data are transmitted to the master. This data may or may
not be the same as with a poll response.
1.3.4 Change-of-State, or COS (not currently implemented)
COS I/O is the function by which a slave device sends its input data to the master when defined
input data changes without the host explicitly requesting it. In the case of a serial device, this may
occur when a new message is asynchronously received from the serial device. This data may or
may not be the same as with a poll response.
1.4 Default Device Configuration
The 1782-JDC DeviceNet address is read from the switches and is set to 63 at the factory. All
other parameters are software settable. The default settings for the 1782-JDC are provided in the
discussion of the Parameter Object.
1.5 EDS
An EDS (Electronic Data Sheet), which describes the various parameters of the 1782-JDC, is
shipped with your device or is available on WRC’s web site: http://www.wrcakron.com/