Figure A-6 Polling Sequence - Microscan MS-3 Manual Book

Chapter A
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 Multi-
drop. The scanner complies with the command when it is polled during the cycle.
Start of Sequence
Concentrator RES 1F REQ
Scanner 02

Figure A-6 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 subse-
quent 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-3 Laser Scanner User's Manual
End of Sequence
STX <T>ETX LRC
1F ACK 1F ACK
Appendices
RES
A-27