User's Manual

i-PORT MB – Manual
Version 1.1 02.02.2007 Page 33/ 37
5.2 Normal initialization (“application on host starting up”)
− Enumerate readers
− check that voltages are OK
− For each reader get serial number and compare to values stored on host.
− Report mismatch as error, if desired automatically redo first time initialization.
5.3 Normal operation (“host application loop after startup”)
− The host application typically polls the readers for data (with the commands “Get Tags” or “Get Tags
Extended”).
− Besides processing these data the host application might routinely log or monitor the uptime of the
readers (parameter 0x02) and the status (parameter 0x04) for error conditions (voltage, crc, timeout).
5.4 Error recovery
Tag data of broadcast tags is inherently acquired without handshake and thus might potentially be missed by
RF detection.
The communication errors on the RS422 lines usually fall into the categories Timeout/Framing Error/CRC
Error/lost character/unexpected characters received. Most probable causes for these are:
− supply voltage at the readers is too low
− dropped characters on host receive side
− cabling problems
− reader malfunction
− Changing reader configuration without knowing of the host application.
As the communication over the serial RS422 link is considered stable and the tag data has been acquired
without handshake the protocol only foresees a retransmit for a single response telegram (firmware revision
≥0.4).
If the data telegrams of the reader are considered very valuable the host program is expected to use the “get
tags extended” telegram which includes the time of first and last detection and a message counter.
On errors the complete data on the reader can be rescheduled for transmission and reprocessed. As error
recovery code is always critical and seldom tested well, this ensures the recovery can be done using the same
algorithm which would be needed for readers which have an intermittent connection to the host.
Connect up to 16 Readers per RS422 line. While the protocol supports more and the signal levels are
refreshed by the daisy-chained readers this limit is imposed the skew between hi/lo and lo/hi transitions on
the data lines. Please note the buffering schemes of the readers allow to significantly reduce the amount of
the transmitted data but the accumulated data rate of events (like newly detected tags or tag re-reporting)
should be lower than the net data rate on the RS422 line.
5.5 How to use inhibits time, re-report interval and list behavior.
When the list behaviour is set to 4  remove tag when reported, the parameters inhibit time and re-report
interval have no influence on the system.
See in the table below for some typical settings: