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ANALYZER OF THE QUALITY OF ELECTRIC POWER SUPPLY
QNA-303 --
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7.- QNA-303 COMMUNICATIONS
One of the main features of the
QNA-303
in terms of communications is the
use of the Z-MODEM protocol, both for the data retrieval and the instrument setting
actions. This protocol is specially designed for the transmission via modem links.
Main features of this protocol are following :
−
Full-Duplex protocol which gets the maximum efficiency from the link.
−
Automatic adaptation of the baud rate to the phone line quality.
−
Automatic adaptation of frame length.
−
Complete system of error detection and correction.
−
The communication is not cut off in case of punctual errors in frames, but
the system tries for several times to resubmit the same information until the
verification of a complete communication interruption.
The application of this protocol assures to get optimum data transmission
times with a minimum number of incidences.
7.1.- Demand format
PROTOCOL: Question / Answer
The demand format is:
$PPCCCAA... ch [LF] (example = $00VER71)
The answer format is:
$PPAA... ch [LF]
$
Any message starts with this symbol (ASCII- 36).
PP
The identification code (00) for the portable
QNA-303
(decimal-ASCII).
CCC COMMAND.
AA
ARGUMENT (Decimal- ASCII).
Ch
CHECK-SUM : Check-sum of all the elements forming the message. It is
calculated by the decimal addition of all the previous bytes in ASCII and then
translating the result into hexadecimal.
Two digits are taken
.
example = $00RAL --> 36 + 48 + 48 +82 + 65 + 76 = 355
355 decimal or 163 hexad. CHECK-SUM = 63
---->
$00RAL63 [LF]
[LF]
LINE FEED indicates the end of the message (ASCII 10).
