Microscan MS-810, User Manual

Page: 131 / 144

Multidrop Communications
MS-810 Industrial Scanner User’s Manual
A-33
Appe
ndices
Appendix M — Multidrop Communications
This appendix describes the rules for setting up a concentrator or controller to communicate
with a scanner in standard Multidrop protocol, as presented in “Protocol Menu,” on page 2-12.
Figure A-11 shows a typical Multidrop network in
which 1 to 50 scanners can communicate with a
host via an intermediary device, a concentrator
or a controller.
Multidrop Addresses
• No two scanner in the Multidrop Network can
have the same address.
• Each scanner in the network must have an
address (from 01 to 50) assigned in its config-
uration program.
Each address has its own separate poll and select
address (from 1C to 7F hex as shown in
Table A-12, “Multidrop Address Charac-
ters”
).
For example, during a polling sequence, Scanner 03 expects a 20 hex (“SP” ASCII poll
character) from the concentrator. And during a select command, it looks for a select value
21 hex (“!” ASCII select character).
Polling Sequence
Data that is transmitted to the host (bar code data, noread messages, counters, etc.) via
concentrators is solicited by poll requests from the host.
The polling sequence example begins with a RES (reset) from the concentrator followed
by poll address 1E (ASCII hex value for Scanner 02) and a REQ (request). The scanner
responds by first transmitting its own address, 1E, followed by a STX (start of text)
character, and then the data. Next it transmits an ETX (end of text) character and an
LRC (longitudinal redundancy check) character.
If the concentrator (or controller) receives the data from the scanner and is able to validate
it with an LRC calculation, it responds with an ACK (acknowledgment). If the scanner in
Scanner 01
Scanner 02
Scanner 03
Host
Concentrator
Multidrop ONLY
RS-485 Interface
Polled Protocol
Concentrator RES 1E REQ ACK
Scanner 02 1E STX DATA ETX LRC RES
Start of Sequence End of Sequence