Microscan MS-890, Руководство пользователя

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MS-890 Industrial Automation Scanner User Manual
A-37
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
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, acknowledging
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 subsequent 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
Polling Sequence
Start of Sequence
End of Sequence