Figure A-10 Polling Sequence - Microscan MS-710 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 scanner complies with the command when it is polled during the cycle.
Start of Sequence
Concentrator RES 1F REQ
Scanner 02

Figure A-10 Polling Sequence

A RES (reset) is the first command in the select sequence. The 1F hex is the select
address associated with Scanner 02 address. It is followed by a REQ (request). The
scanner 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 scanner replies by transmitting its own address, followed by an ACK, acknowledg-
ing receipt of the command. Upon receipt of an ACK, the concentrator concludes the
successful exchange with a RES.
In the example above, the scanner 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 subsequent poll it would send 02T/00012. (The 02 at the
beginning of the string is the scanner's address.)
Select Reset
If the scanner 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.
MS-710 Scanner User's Manual
A-32
End of Sequence
STX <T>ETX LRC
1F ACK 1F ACK
RES