Microscan MS-4 Dokumentacja Pobierz pdf (Strona 195)

Chapter A Appendices

MS-3 Laser Scanner User’s Manual A-27

A–Appendices

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.

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.

Concentrator RES 1F REQ STX <T>ETX LRC RES

Scanner 02 1F ACK 1F ACK

Start of Sequence

End of Sequence

Figure A-6 Polling Sequence

1 2 ... 190 191 192 193 194 195 196 197 198 199 200 201 202

Brak uwag

Microscan MS-4 Dokumentacja Strona 195