Western Reserve Controls 1782-JDO Uživatelský manuál stáhnout pdf (Strana 26)

Western Reserve Controls, Inc. 1782-JDC User’s Manual

the JDC. If you need to transmit on the ASCII link, you will need to use the polled connection

to do so. The polled and cyclic connections are not exclusive, so both can exist at the same

time. The manner in which cyclic connection reports its data is the same as the polled

connection. The cyclic connections transmit buffer is the same as the polled connections

transmit buffer, so overflows and received delimiters act the same over any connection.

The Change of State (COS) connection is the same as the cyclic connection except that

as well as triggering communications on the expiration of the timer, the COS connection also

initiates a transfer on a receive of the delimiter or an overflow. The COS connection is

mutually exclusive with the cyclic connection, but can coexist with the polled connection. The

COS connection operation is very useful in conserving bandwidth, and provides the Master

with the most current data as fast or faster than a poll connection. The COS connection

automatically turns on the COS mechanism when the connection is created.

5.2.3 Setting up the DeviceNet I/O Connections

It is useful to first set up your serial link before setting up your connection. To set up the

communications with your network configuration tool, it is often necessary to know the

connection input and output sizes. Instructions for setting up your serial connection are

provided above. See the sections on receive and transmit sizes.

If you are using a network configuration tool with some type of scanner or scanning

software, you must direct your scanner to set up the connections for you. This often requires

some information about the device, such as input and output sizes. The input and output

sizes are computed from the transmit size and the receive sizes. These sizes are defined in

the parameter object of your device. The transmit size of the poll connection is computed by

adding 2 to the transmit buffer size on the 1782-JDC. The Transmit size for the change of

state and cyclic connections are set to 0, because these connections do not initiate a

transmission on the serial link. The receive size of all three connections is computed by

adding 3 to the receive buffer size.

Important: Remember to re-map the data (if necessary) after you set the sizes, because

many configuration tools will automatically unmap your data when you change the connection

sizes. If you are not using such a software package, it is probably not necessary to set up the

transmit and receive sizes.

5.2.4 Setting up the Connection Timer (EPR)

EPR stands for Expected Packet Rate. This is the value that the JDC sets the connection

timer to for the cyclic and polled connection. This is also the value it uses in the connections

to calculate the time the device should wait before signaling a timeout. If you have a scanner

or scanning software, you must configure it with the EPR that you want the JDC to be

scanned with. The scanner will then configure the EPR in the JDC at the beginning of

communications. Consult your scanner’s manuals on how to configure the EPR (the EPR is

sometimes referred to as the “scan rate”).

Note: If you need to set up the EPR, it can be done manually by performing a set (Service

hex

) on the connection class (Class 5

hex

) attribute 9. The polled connection uses instance 2,

where as the COS and cyclic connections use instance 4. This must be done after allocating

the connection.

5.2.5 Autobaud Operation

Autobaud is the mechanism that allows the DeviceNet device, in this case the JDC, to

automatically determine the baud rate that is operational on the network to which the JDC is

connected and adjust its DeviceNet speed to match. The JDC is shipped with autobaud as its

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