Figure A-8 Select Sequence - Microscan MS-3000 User Manual

Select Sequence
Unlike poll requests, select commands always originate from the host and
consist of serial configuration or operation commands to devices that are
configured in Multidrop. The decoder complies with the command when it is
polled during the cycle.
Figure A-8 is an example of a select sequence.
Start of Sequence
Concentrator RES 1F REQ
Decoder 02

Figure A-8 Select Sequence

A RES (reset) is the first command in the select sequence. The 1F hex is the
select address associated with Decoder 02 address (see
A-20). It is followed by a REQ (request). The decoder responds with its own
select address, 1F hex, and an ACK (acknowledge). 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,
acknowledging receipt of the command. Upon receipt of an ACK, the con-
centrator 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 scanner'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 scanner's address.)
Select Reset
• 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.
1. For additional information on Multidrop, see the MS-5000 Multidrop Concentrator Us-
er's Manual.
MS-3000 Single Head Decoder User's Manual
Multidrop Communications
End of Sequence
STX <T>ETX LRC
1F ACK 1F ACK
table A-6 on page
1
RES
A-19