Microscan Quadrus EZ, Руководство пользователя, Страница: 339 / 366

Quadrus EZ Reader User’s Manual
A-35
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 Multidrop. The
reader 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 Reader 02 address. It is followed by a REQ (request). The reader
responds with its own select address, 1F hex, and an ACK (acknowledge). The concentra-
tor then transmits an STX (start of text), the data (in this case a <T>), an ETX (end of text),
and an LRC character.
The reader replies by transmitting its own address, followed by an ACK, acknowledging
receipt of the command. Upon receipt of an ACK, the concentrator concludes the success-
ful exchange with a RES.
In the example above, the reader 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 reader’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 reader’s address.)
Select Reset
If the reader 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
Reader 02 1F ACK 1F ACK
Start of Sequence
End of Sequence
Polling Sequence