Microscan MS-5000, User Manual, Page: 27 / 94

Standard Single Concentrator Network
MS-5000 Multidrop Concentrator User’s Manual
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knowledge). The concentrator then transmits an STX (start of text), the data
(in this case a <T>), an ETX (end of text), and an LRC character.
The decoder replies by transmitting its own address, followed by an ACK.
With an ACK the decoder acknowledges receipt of the command. Upon re-
ceipt of an ACK, the concentrator concludes the successful exchange with a
RES.
In the example above, the decoder only
acknowledges a trigger counter
request from the concentrator. It does not respond to the trigger counter
request until a subsequent poll. For example, if the decoder’s trigger count
was 12 at the time the trigger counter request was received, on a subse-
quent poll it would transmit 02T/00012. (The 02 at the beginning of the
string is the decoder’s address.)
Note : Data in select command strings to decoders cannot contain characters
that match the host-to-concentrator ETX character or the command will be ter-
minated prematurely. For example, if a concentrator’s ETX is the default car-
riage return character and you attempt to send a carriage return through the
concentrator to a decoder, the concentrator will interpret the carriage return as
its own ETX character and terminate the command.
Select Reset Sequences. Both the concentrator and the decoder can ter-
minate the select sequence by transmitting a RES (reset) to the other
device. The following applies:
• If the concentrator does not receive a response from the decoder after
transmitting a select request (RES SEL REQ), the concentrator will wait
for its time out and then retry the request. It will retry the request three
times before advancing to another device.
• If the decoder receives bad data from the concentrator, it transmits a SEL
(its select address) and a NAK to the concentrator. The concentrator re-
transmits the data up to three times. The concentrator will end the
sequence with a RES (reset) if no ACK is received.
• If the concentrator transmits data to the decoder, and the decoder
responds with an ACK or NAK, but the concentrator misses the decoder's
response, the concentrator will timeout and transmit a REQ to the
decoder, requesting another response to its transmission. If after three
requests the concentrator does not receive an ACK, it will end the trans-
mission with a RES (reset).
ETX Character. Select commands (or select multiple commands) from the
host to any address must end with an ETX, if defined. The default ETX
character is a carriage return (CR). It can be changed to any ASCII charac-
ter or nulled (undefined) in the concentrator configuration program.