7ML19985CN01 Milltronics SF 500 - INSTRUCTION MANUAL Page 89
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Communications
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
Configure modems 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.
For a typical dial-up modem, try the following setup as a first attempt:
Master
Modem
• auto answer off (dip switch?)
• load factory default (dip switch?)
• no flow control (dip switch?)
• baud rate = 9600
• 10 data bits (probably the default)
Modbus RTU Software
• baud rate = 9600
•8 bit
• no parity
•1 stop bit
• dial prefix: ATDT
• Initialization command: ATE0Q0V1X05=0512=100
• Reset command: ATZ
• Hang-up command: ATHO
• Command response delay: 5 seconds
• Answer Delay: 30 seconds
• Inter-character delay: 55 ms
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