GE GEK-106273L Instruction Manual page 188

ANNEX 4 MODEM CONNECTION
14. ANNEX 4. MODEM CONNECTION
If we wish to connect the relay to a remote PC, it will be necessary to previously link two modems to the telephone
line. The modem on the relay side will receive the call, and the modem on the PC side will make the call.
This way, both modems will be configured in different ways: the modem on the PC side will receive the commands
from the PC for starting or ending communication, and therefore it will make the call. The modem connected to the
relay will not receive any command from it; it will only accept communication whenever it is requested. Therefore, this
last modem will be configured in "dumb" mode, which means that it does not receive commands, and is in auto-reply
mode.
The ENERVISTA MII SETUP is a DCE device (Tx=3, Rx=2 signals), so as regards TX and RX it works as a modem
(which is also a DCE device). Therefore, it is not necessary to cross the TX and RX signals in direct connection to the
PC, which is a DTE device (TX=2, RX=3 signals). However, in case of a connection via modem, it will be necessary
to cross the wire in the relay by means of a null modem, so that RX and TX signals are inverted, as we will be
connecting two DCE devices.
In addition, we must check whether the relay is directly connected to the modem via its RS232 port, or via an
RS232/RS485 converter. In this last case, we will have to verify whether the converter output is DTE or DCE, and use
a null modem in the second case. For example, the DAC300 converter incorporates two ports, a DCE and a DTE. In
the case of a F485 converter, an internal selector detects whether it is connected directly to a modem or relay (DCE)
or to a PC (DTE).
As regards the modem-modem, PC-modem, and Relay-modem communication baud rates, in the first cases, it is
recommended to be set at the same baud rate as the relay. The baud rate between relay and modem will always be
the one set for the relay.
In case of communication problems between both modems, it is recommended to reduce the line baud rate.
14.1 HAYES MODEM
In order to establish communication between two HAYES modems, both of them must accept HAYES commands.
This is compulsory, as the PC will send specific commands for this type of modem. We must place the AT command
before every command. It is possible to group several commands inside an only command line (e.g. ATB1 and ATE1
equals ATB1E1).
However, we must take into account that each manufacturer will implement only one sub-group of the HAYES
commands, and therefore we cannot indicate an initiation command valid for every equipment. It is the customer's
responsibility to determine which commands are accepted by a particular modem.
As a general rule, it is recommended to disable any data compression, hardware protocols, flux control or error
control. Some modems allow a command, e.g. &Q0, which selects the direct asynchronous mode.
The local modem configuration, that is, the configuration of the modem that makes the call, will be performed by
ENERVISTA MII SETUP software, by means of the provided initiation command. In order to configure the remote
modem (connected to the relay), we need a communications program that allows sending HAYES commands. Any
®
Windows version includes a program called HYPERTERMINAL (HYPERTRM.EXE) which allows to send HAYES
commands by the selected serial port. Besides, we can use any communications program allowing sending
commands, such as Procomm Plus or LAPLink. Once the modem is connected to the selected port in the program,
and after setting the communication parameters, we can send the required commands.
Later in this document we will detail the configuration that must be entered in some HAYES modems already tested.
GEK-106273L MIF Digital Feeder Protection 14-1