Справочное Руководство для LXE 1280
Message Format
119
E-SW-LDSPLUSRG-G
LDS Plus Reference Guide
Sequence Numbers from the Host
If the DOS terminal expects to receive sequence numbers, the host must generate the character for
the sequence number. The host computer increments the sequence number with each new message
transmission to the same DOS terminal.
the sequence number. The host computer increments the sequence number with each new message
transmission to the same DOS terminal.
The host may send printable characters A-Z, a-z, 1-7, or any mix as subsequent sequence
numbers.
numbers.
If the network device...
Then the host...
acknowledges the message
increments the sequence number by one each time it
sends a new message to the same DOS terminal.
sends a new message to the same DOS terminal.
does not acknowledge the message
and the host must retransmit it
and the host must retransmit it
does not increment the sequence number to that
DOS terminal.
DOS terminal.
When the DOS terminal parameter RcvSeqNumbers is set to yes, the DOS terminal interprets the
first text character of any message from the host computer as the sequence number.
first text character of any message from the host computer as the sequence number.
The DOS terminal compares the character in the first text position with the character that occupied
this same position in the previous message. If these characters are the same, the DOS terminal
recognizes it as a duplicate message and discards it. If the characters are different, the DOS
terminal discards the sequence number and displays the message.
this same position in the previous message. If these characters are the same, the DOS terminal
recognizes it as a duplicate message and discards it. If the characters are different, the DOS
terminal discards the sequence number and displays the message.
Here is an example of an outbound message with a sequence number:
The host computer generates
sequence number
sequence number
6
from the automatic
counter.
<02SiD
6
5B]PART _ _ _ _ TO BIN3 AISLE4C
R
L
F
Figure 4-20 Outbound Message with Sequence Number
Sequence Numbers to the Host
The host computer must accept sequence numbers when the DOS terminal sends sequence
numbers. A sequence number prevents the host computer from acting upon duplicate messages.
numbers. A sequence number prevents the host computer from acting upon duplicate messages.
When the host receives a sequence number from a DOS terminal, the host should be programmed
to compare the sequence number of the current message to the sequence number of the previous
message from the same terminal ID. If the sequence number is the same, the host should discard it
because it is a duplicate message.
to compare the sequence number of the current message to the sequence number of the previous
message from the same terminal ID. If the sequence number is the same, the host should discard it
because it is a duplicate message.
Here is an example of an inbound message with a sequence number:
The automatic counter in the terminal
generated sequence number
generated sequence number
3
.
<02MA
3
4) PART 1234 TO BIN3 AISLE4C
R
L
F
Figure 4-21 Inbound Message with Sequence Number