Western Reserve Controls, Inc.
1782-JDO User’s Manual
PRELIMINARY
21
5.2.3 Reading the I/O Poll Data Size
This is the number of bytes that the JDO will receive from the DeviceNet Master and is
determined by:
consume_size = number_of_B1s * 2
This number is calculated by the JDO. The valid settings for this value are 2-40. The default
value is 2. This consume_size is used to set up the Poll transmit size at your Master device.
These values can be retrieved by using the standard get service on class 15 (F
hex
), instance
6, attribute 1 (See Table 5-1).
Note: There are always 2 bytes allocated for output data for each B1, irregardless of
how many or whether any channels are configured as outputs.
5.2.4 Setting up the DeviceNet Baudrate
If you wish to change the baudrate to a fixed speed, you can set it in two different places.
The first is the standard location for the DeviceNet baud rate, which is in the DeviceNet
object. This is where most configuration tools will look to change the baudrate. This is fine on
normal DeviceNet systems, however the JDO provides some extended DeviceNet
functionality above normal systems to allow the Autobaud functionality. This extension is not
defined by ODVA thus cannot be attached to any of the standard DeviceNet objects to
ensure compatibility. You can still use the baudrate in the normal manner; it will just not allow
the Autobaud setting.
This value can be set and retrieved by using the standard set and get services on class 15
(F
hex
), instance 3, attribute 1. (See Table 5-1).
5.2.5 Autobaud Operation
Autobaud is the mechanism that allows the DeviceNet device, in this case the JDO, to
automatically determine the baudrate that is operational on the network to which the JDO is
connected and adjust its DeviceNet speed to match. The JDO is shipped with Autobaud as its
default baudrate.
5.2.6 Setting up the Connection Timer (EPR)
EPR stands for Expected Packet Rate. This is the value that the JDO 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 JDO to be
scanned with. The
scanner will then configure the EPR
in the JDO 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
10
hex
) on the connection class (Class 5
hex
) attribute 9. The polled connection uses instance 2.
This must be done after allocating the connection.
