PL-565 Accumass BW500 Page 133
Communications
Modems
The BW500 has been successfully connected to several different modems. In
general, the Modbus protocol is a very modem friendly protocol. This section gives
some general guidelines on modems and their connection. For detailed information,
see the modem documentation.
Picking Modems
There are several different types of modems; dial-up, leased line, radio-link, fiber-
optic to name the most common.
Dial-up
uses a standard analog phone line and dials the number of the receiving modem.
Lease line
come in either 2 or 4 wire types and use special phone lines that are ‘leased’ from
your phone company (or you) and do not require any dialing.
Radio-link
come in many different types, but all use radio frequencies for transmitting the
information.
Fiber-optic
uses a fiber-optic line to connect the two modems.
Each type of modem and each model have various characteristics. Before
purchasing the modem contact the modem manufacturer and ask if they have had
experience using the modems with Modbus protocol with no flow control. If they
have, ask them what settings were required.
Setting up the Modems
Modems can be configured using software, dip switches, jumpers or a combination.
Dip switches are normally located at the back of the modem, jumpers are normally
located on the motherboard and require that you remove the cover. Software
normally requires you to use a standard terminal program and to connect to the RS-
232 port on the modem and send special commands. The most popular command
set is called the AT, or Hayse, command set.
Your modem manual should give details on how to configure it.
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