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• Make a data call to cellular phone number with the modem;
• After the reception of the “CONNECT” notification string
(i.e. the data connection establishment), wait for the string
“RDY<CR>” issued by the interface: this means that the
interface is ready to receive a command from the remote PC;
• If the password was enabled in the phone interface during
last configuration (see “Interface configuration”), the appli-
cation software must send the password within 3 minutes
through the command “PWD<interface password><CR>”
and the interface will answer <ACK> (char 0x06) if the pass-
word is correct, or <CAN> (char 0x18) if password is not
correct, or <NAK> (char 0x15) if command syntax is wrong,
and hangs up the call when 3 minutes have elapsed.
Local channel selection
Before communicating with one of the loggers attached to
HI504903
, the application software on remote PC needs to
specify to the interface to use the RS485 channel with 1200 bps
(this is baud rate used by interface to communicate with
HI142
during polling procedure). To do this, the C
0A
<CR> com-
mand has to be sent to
HI504903
. The cellular phone interface
will send back <ACK> if the command is correctly recognized,
otherwise <NAK>. <CAN> is sent back if the required chan-
nel is not configured in the instrument. When command is
correctly recognized, baud rate in the local PC must be set to
1200 bps. In this way the local PC and the selected instrument
are connected directly and everything works like a direct point-
to-point connection (if we exclude the delay issues).
Remote channel selection
Also in remote communication session the application software
needs to select a channel, but the procedure is a bit different
from the local one. Before communicating with one of the in-
struments attached to
HI504903
, the application software on
remote PC needs to specify to the interface to use the RS485
channel with 1200 bps. To do this, the C
0A
<CR> command
has to be sent to cellular interface. The phone interface will
send back “+++” (the “+++” is needed to return tempo-
rarily to command mode in the cell phone to change baud
rate) and then, after several seconds, <ACK> if the command
is correctly recognized, otherwise <NAK>. <CAN> answer is
sent back if the required channel is not configured in the instru-
ment. When command is correctly recognized, the local PC
and the selected remote instrument are connected directly and
PC COMMUNICATION PROTOCOL
Even if it is strongly recommended to use
HI92140
software
to establish local or remote connections between
HI504903
and a PC, it is possible to try also without
HI92140
by build-
ing the application software for communication session
management (i.e. session establishment, serial port channel
selection and session termination). It is necessary to issue to
the interface towards PC some simple commands accom-
plishing with the protocol implemented on
HI504903
.
Commands are composed of three parts: command identi-
fier, parameter (when needed), end of command. The end of
the commands corresponds to the CR char (0x0d).
Following is the complete list of available commands:
Command
Parameter
Remarks
PWD
<interface password>
Send the general password (*)
C0A
not available
Request to RS485 channel selection
(*) 6 to 20 characters long ASCII string representing interface
password (letters in uppercase format)
Local PC connection session establishment
To start a local PC connection the application software has to
perform the following operations on PC side:
• Set baud rate at 9600 bps on the selected PC serial port.
• Pull up the DTR line of the serial port and wait for phone
interface “RDY<CR>” answer. The DTR line must remain
high while application software is running; if the DTR goes
down while communication is taking place, then
HI504903
aborts immediately the current PC communication session.
• If the password was enabled in the phone interface during
last configuration (see “Interface configuration“ section), the
application software must send the password through the com-
mand “PWD<interface password><CR>” and the interface
will answer <ACK> (char 0x06) if the password is correct, or
<CAN> (char 0x18) if password is wrong or <NAK> (char
0x15) if command syntax is wrong.
Remote PC connection session establishment
To open a remote PC connection the application software has
to perform the following operations on PC side:
• Set the baud rate at 9600 bps for the serial port where mo-
dem is connected and continue to use this value for
all the
time
the communication is in place;
