HORNER HE800JCM200, Руководство пользователя

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CH. 2 14 MAY 2002 PAGE 9
MAN0484-01
CHAPTER 2: OPERATION
2.1 General
Chapter Two covers operational information for the JCM200.
2.2 Two Communication Methods for Handling Data
The JCM200 can request and monitor data from and transmit data to devices on the J1939 network.
There are two communication methods used for handling data. The first method is
Scanning in which
Parameter Group Numbers (PGNs) are pre-configured, and the module continuously gathers data for the
configured PGNs. The second method is a
Transmit Channel in which a message is built in PLC
registers and is transmitted onto the network. The following sections cover each communication method
in detail.
2.3 Scanning
The Scanning method uses a scan table that contains a series of PGNs and associated information.
Data for the configured PGNs is continuously gathered and sent to the PLC. There are two modes for
gathering data from devices on the J1939 network, monitor and request. Each PGN in the scan table is
configured to use one of the two modes for gathering data. The JCM200 does not know which PGNs
require monitoring and which PGNs require requesting; it is the responsibility of the individual configuring
the module to enter the information. Otherwise, the data may not be updated.
a. Monitor Mode
An engine control module (ECM) sends some PGN data onto the network at regular intervals. The
specific PGNs that are sent vary between ECMs. If the ECM broadcasts a desired PGN’s data on a
regular basis, then the mode for that PGN is configured for monitor.
Monitoring does not require interaction between the JCM200 and a device on the network. The JCM200
monitors the network for the PGNs that are configured as monitor mode in the scan table. If it finds a
match, then the data is sent to the PLC.
b. Request Mode
If the desired PGN is not sent on a regular basis, then a request must be made from the JCM200 to the
device
before the data is sent. The mode for these PGNs are configured for request.
Requesting requires interaction between the JCM200 and a device on the network. The JCM200 must
send a request message to a device onto the network and receive a reply
before that data can be sent to
the PLC.