Burster DIGISTANT 4420-V001, Руководство по эксплуатации, Страница: 83 / 146

Model 4420-V001 DIGISTANT
®
Page 83
After link establishment in accordance with the ANSI X3.28 Subcat 2.5
protocol, the data is transmitted in accordance with Subcat. A3 or Sub-
cat. A4 (corresponding to A3 with an additional block-check character).
Subcat. A3/A4 is used in systems where a master station sends data
to a single slave. The master station sends every message to the slave
station and waits for a response. If the response indicates that the data
was accepted (ACK), the master station can send another message or
terminate the link. A negative response (NAK) from the slave station
indicates to the master station that the data was not understood.
Data transmission
Data trsnamission is commenced by the master station after link estab-
lishment (see Subcat 2.5). The master station starts transmission with
<STX>. The required data is sent subsequently. The data block ends
with <ETX>. During transmission in accordance with Subcat. A4, <ETX>
must be followed by the block-check character (BCC).
Response
After recognizing <ETX> or <BCC>, the slave station sends one of two
possible responses:
( 1 ) If the data was accepted and the station is ready to
receive new data, it sends <ACK>. After that, the master
station can either send the next batch of data or end the
transmission.
( 2 ) If the data was not accepted and the slave station is ready
to receive new data, it sends <NAK>. After that, the master
station can send other data or terminate the link.
If the master station receives no response or an invalid one, it can
send a "Reply-Request Supervisory Sequence" consisting of <ENQ>
or terminate the link.
Explanation
of the data
transmis-
sion proto-
col in accor-
dance with
ANSI X3.28
Subcat A3/A4
Link
termination
Termination
The master station sends <EOT> to indicate that it does not have
any more data to transmit. <EOT> transfers master status back to the
control station.