BS ISO 11783-4 pdf download – Tractors and machinery foragriculture and forestry-Serial control and communications data network Part 4: Network layer.
When an NIU forwards (7,1 Repeater and 7.2 Bridge) a message to another segment in the same address space, it uses an address identical to that of the onnalor ol the message. Ordinarily, this does not cause arbitration problems, as the unit will not retransmit the message to the segment it onginaly came from and, moreover, the addresses are unique on a given ISO 11783 network,
The sole exception is when an address-claim message is forwarded to a segment in which another CF is simultaneously claiming the same address. In sudi a low-probability situation, the NIU should stop the automatic retransmission sequence withifl the CAN protocol chip, Otherwise, the NIU will experience multiple collisions and go bus off’, thereby preventing other messages from being forwarded until the NIU is able to recover from the bus off condition.
An NIU may begin to forward messages from one segment to anolhei’ before the NIU has claimed an address (i.e. It does not perform address translations) If Ills amply acting as a repeater or bridge
MOTE Until an NIU has corrted a poaer up sequence and connected ii to the network. the subnetwoi’k and the CFs connected to it cannot receive other messages.
6.2 FilterIng
62.1 General
For the filtenng function, messages sent with Transport Protocol, Extended Transport Protocol. Fast Packet, or other message packeting mechanism, shall be handled according to the parameter ‘oup number (PGN) of the contained message. If the PGN of the contained message Is defined for the filter, the protocol handling messages shall be processed according to the defined filter.
6,2.2 Block mode
In block filter mode (0). the NIU shal default to forwarding all messages (7.2). Bus utilization (traffic) can be higher on each bus segment, but if it is within acceptable limits, the message filtering algorithm will be nonexistent. The filler database within the NIU can contain identifier entries (PGN values) for messages whid’i shall not be forwarded (blocked). This can be used to reduce the overal bus traffic on a given segment, and is the preferred mode of operation for bridges conforming to ISO 11783. Filter database entries are typically made during assembly or initial configuration and retained in non-volatile memory.
6.2.3 Pass mode
In pass filter mode (1), the NIU shall default to not forwarding messages (7.2). Then, in order for a message to be forwarded. an entry shall exist with a specific identifier (PGN value) for that pactioular message. This mode is best for ports on NIUs that link subnetworks performing specific functions. It requires prior knowledge 01 the CFs and the functions of the whole network, or that the CFs be able to add entries to the filter database, in Which case the NIU can require more memory and processing power if it is to accommodate a large filter database Moreover, some entries within the database need to be permanent (I.e. configured to be always present), so that corresponding messages are always forwarded across the whole network, Typical applications are network management. dtagnostics and global requests.
6.3 Address translahon
An NIU can provide address translation for particutar messages (7,3), permitting a single address to be used for referencing a particular segment (implement) even without knowledge of a particular function address (lighting) on the segment. For this, an address translation database shall exist in order to identity, through a iook-up table, the corresponding source address or destination address The NIU is required to have a valid daimed address before it can provide this service.
6.4 Message repackaging
An NIl) can repackage messages (7.4) when transferring them from one segment to another. This provides a potential reckiction in bus traffic by improving the amount of useful parameters per message, while reducing the number of different messages received by a particular CF. A message repackaging database or processing routine should exist in order to determine how the messages are to be repackaged,
6.5 Network message
6.5.1 Network message PGN
The PGN for the network message is shown in Table 1.
BS ISO 11783-4 pdf download – Tractors and machinery foragriculture and forestry-Serial control and communications data network Part 4: Network layer
