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XDT User’s Manual Appendices
52
Appendix K: RS-232C Interface Protocol
The instrument uses a simple protocol to communicate to a host computer through its RS-232C
interface, see section 3.3.2.5 for electrical connections. The interface is configured as 9600 baud,
Even Parity, 8 Bits, 1 Stop; and it echoes all received characters.
To illustrate the protocol, the following notation conventions are used in this section:
The characters sent or received are depicted in bold. Send refers to sending from the host com-
puter to the XDT. Receive refers to receiving from the XDT into the host computer. The com-
mands and arguments are shown in capital letters while place holders for choices are labeled with
lowercase italic letters, with the allowed characters shown below, “nn” denotes a numeric value.
Bytes which are not characters are shown with diagonally placed mnemonics, for example Escape
is depicted as
E
S
C
, this signifies a single byte (hex 1B). Optional characters or command argu-
ments are encompassed with brackets [ ].
The commands may be sent in either upper or lower case. Arguments may be delimited with
space or comma.
HELP command
Lists all of the available commands.
send: H[ELP]
C
R
receive: Help ? Data SN
C
R
L
F
Who Reset Login
C
R
L
F
DATA command
Selects the reporting format of the current measurement.
This formatting will be retained until the next DATA command even if the power is turned off.
send: DA[TA] units [interval [mode]]
C
R
CnnN
FG
P
L
G
D
U
The units argument selects the units in which the measurement will be reported.
C,F,P,L & G select the dewpoint in °C,°F,ppm,Lbs H
2
0/mmscf and gm/m
3
respectively.
D selects decibels which is the measured sensor attenuation.
U selects using whatever units are selected by the user on the display.
The interval argument is optional, if it is not entered then the measurement will be reported only
on a query with the “?” command. However if it is desired for the unit to report the measurement
on a regular interval without a query then an interval in seconds may be specified in the range 1 to
255 seconds. This feature allows the user to log the measurement on a dumb terminal or a printer.