Figure A-12 Select Sequence - Microscan MS-615 User Manual

Table of Contents

Appendices

Scanner 02) and a REQ (request). The scanner responds by first transmit-

ting 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 turn receives the ACK, the scanner

ends this successful exchange with a RES (reset).

Polling Reset

• If the scanner has no information, it responds to a poll request by transmit-

ting a RES (reset).

• If the scanner receives a NAK instead of the ACK after transmitting its

data string, it will re-attempt to transmit the data string up to three times. If

the scanner still does not receive an ACK, it will transmit a RES (reset)

and discard the data in its buffers.

• If the scanner transmits data to the concentrator and the concentrator

responds with an ACK or NAK, but the scanner doesn't receive the concen-

trator's response, the scanner will timeout and transmit a REQ to the con-

centrator and request another response. If after three retries (the number of

times it transmits a REQ to the concentrator) the scanner receives no

response, it ends the transmission with a RES (reset).

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.

Figure A-12 is an example of a select sequence.

Concentrator

Scanner 02

A RES (reset) is the first command in the select sequence. The 1F hex is the

select address associated with Scanner 02 address (see table A-7 on page

A-18). It is followed by a REQ (request). The scanner responds with its own

A-16

MS-610 Scanner User's Manual

Start of Sequence

RES 1F REQ

STX <T>ETX LRC

1F ACK