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Appendix B. Advanced Setup Menu

B.2 Error Handling and Retries

In the RF module received packets are analyzed for data corruption with an

embedded CRC. The radio rejects a received packet (doesn’t send it out a port) if

the packet’s header address fails to match the radio address, if an RF module receive

error is detected, or if the RF packet’s CRC test fails.

B.2.1 Number of Retries

This setting specifies the maximum number of times an RF401 will re-send a packet

failing to get an ACK response. The default setting is zero which inactivates retries.

The allowable range is 0 to 255. Entering a number greater than zero activates

retries. A receiving radio responds to the sending radio with an ACK packet for

every RF packet that it receives, addressed to it, that has a valid CRC.

B.2.2 Number of Time Slots for Random Retry

This setting is active when the Number of Retries is greater than zero. It specifies

the number of 38 ms time slots to create among which to randomly re-send a packet

which has failed to get an ACK packet response. The allowable range is 0 to 255.

If packets are failing because of periodic noise or signals, specifying more time slots

for random retries will improve the chances for successful retry packet delivery.

Increasing the number of time slots, however, results in longer average retry delays

which will lower data throughput.

B.2.3 Number of Bytes Transmitted before Delay

This feature prevents radios which have lots of data to transfer from tying up a

network until it is finished. The range of settings is 1 to 65535. The default value is

400 (bytes). This setting forces an RF401 to pause long enough, after sending the

specified number of bytes, for another radio to send some data.

B.2.4 Sync Timer Setting

This setting determines how often sent packets will include hop synchronization

information in the headers. The default setting is 0 which specifies that every packet

will contain hop sync information. A value greater than zero specifies the interval at

which a packet will contain hop sync information. The allowable range is 0 to 255

in units of 100 ms. All radios in the network should have the same Sync Timer

Setting.

For example, if you input a value of 50, then packets with hop sync info will be sent

out every 5 seconds improving (shortening) the response time of a transmit/response

sequence. Even though this shortens the time required to send x amount of data, the

throughput is still affected by the CS I/O or RS-232 port baud rate setting.

B.2.5 Number of Retry Failures

This reading is available in Setup Menu/Advanced Setup/Radio Parameters/Radio

Diagnostics. It indicates the number of times that the RF401 has re-transmitted the

specified Number of Retries but failed to get an ACK packet from the receiving

radio. For example, if the Number of Retries is set to 3, the transmitting radio will

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Campbell RF400 Handbuch Seite 55