Hanna Instruments HI 504901 User Manual

Page 25

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” answer. The DTR line must remain
high while application software is running; if the DTR goes
down while communication is taking place, then HI504901
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” and the interface
will answer (char 0x06) if the password is correct, or
(char 0x18) if password is wrong or (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;

• Make a data call to the cellular phone number using the

modem;

• After the reception of the “CONNECT” notification string

(i.e. the data connection establishment), wait for the string
“RDY” 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” section), the
application software must send the password within 3 min-
utes through the command “PWDpassword>” and the interface will answer
(char 0x06) if the password is correct, or (char
0x18) if password is not correct, or (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 instruments attached to
HI504901, the application software on remote PC needs to

PC COMMUNICATION PROTOCOL

Even if it is strongly recommended to use HI92500 software
to establish local or remote connections between HI504901
and a PC, it is possible to try also without HI92500 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 HI504901.
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

Send the general password (*)

N R

Request to channel selection (**)

DSC

not available

Request to disconnect from present
channel selection

(*) 6 to 20 characters long ASCII string representing interface

password (letters in uppercase format)

(**) NR are ASCII characters corresponding to the channel

(N) on the interface where is attached the instrument(s)
with which the application software wants to communicate
and the baud rate used (R) for communication with the
corresponding device(s).

The character N for requested channel is coded like this:

N code

Selected port

RS485

RS232 channel 1

RS232 channel 2

The character R for requested channel is coded like this:

R code

Baud rate value

1200 bps

2400 bps

4800 bps

9600 bps