Thermo Scientific AutoWAVE 1-0479-013, Руководство пользователя

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Document 1-0479-013 Rev B
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(2) Max Slave Retry
(3) Retry Odds
While packets transmitted from the master to the slaves in a Multipoint network are not
acknowledged, packets transmitted from slaves to the master are. However, it is possible
that more than one slave will attempt to transmit to the master at the same time, and it is
therefore important that a protocol exists to resolve contention for the master between slaves.
This is addressed through parameters (2) Max Slave Retry and (3) Retry Odds. The Max
Slave Retry setting defines how many times (0 to 9) the slave will attempt to retransmit a
packet to the master before beginning to use a back-off algorithm. Once the slave has
unsuccessfully attempted to transmit the packet the number of times specified in Max Slave
Retry it will attempt to transmit to the master on a random basis. The Retry Odds parameter
determines the probability that the slave will attempt to retransmit the packet to the master;
a low setting will assign low odds to the slave attempting to transmit and conversely a high
setting will assign high odds. An example of how this parameter might be used would be
when considering two different slaves in a Multipoint network, one close in with a strong
RF link and the other far from the master with a weak link. It may be desirable to assign
higher Retry Odds to the slave with the weaker link to give it a better chance of competing
with the closer slave for the master’s attention.
(4) DTR Connect
Another parameter in a Multipoint network is (4) DTR Connect. When set at 1 the slave will
connect to the master if it is free when the DTR line goes high on the RS-232 connector. In
setting 2 the transceiver will accumulate data in its buffer and transmit in a burst when the
buffer is full. This mode is valuable when a network has many low data rate devices and it
is desirable to increase overall network capacity. In setting 0 the transceiver will transmit
when RS-232 data is received.
(5) Repeater Frequency
The repeater’s hopping pattern must also be set in a Multipoint network; this is accomplished
with parameter (5) Repeater Frequency. Setting this parameter is in contrast with point-to-
point mode where the repeater automatically uses the master’s hopping pattern. The repeater
may be programmed to either use the master’s hopping pattern (selection 0) or its own
(selection 1).
(6) Network ID
Option (6) Network ID allows Multipoint networks to be established without the use of the
Call Book. If the Network ID is set to any value lower than the default (255) the slaves in
the Multipoint network will communicate with the first Multipoint master or repeater heard
with the same Network ID. When the Network ID is used; Multipoint masters and repeaters
may be replaced without reprogramming all of the slaves in the network. In addition, this
allows a slave to establish communications with different masters, (though not at the same
time), without having the ID (serial numbers) in the Call Book. This is very useful in mobile
Multipoint applications.