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When planning an RS-485 installation, consider the following:
Table 2-4.
RS-485 hardware
• Every piece of equipment must have a unique address.
• Every piece of equipment must remain quiet while waiting for a
command.
• All interface wiring and RS-485 transceivers must be correctly installed.
Note that there are both 2-wire and 4-wire RS-485 implementations.
®
Although the IQ plus
wire equipment in the system by tying the two transmit (A) pins together
and the two receive (B) pins together.
Table 2-5.
RS-485 software
• The controller software must be compatible with the IQ plus 800/810's
protocol. Some equipment may have its own, proprietary RS-485
protocol.
• All equipment in the RS-485 network must follow the rules of half
duplex communications: "Be quiet unless spoken to;" and "Never echo
back what you are receiving."
• The controller must turn on its transmitter, send the commands, wait for
the transmission, and finally, turn off its transmitter.
• The controller software must be able to handle the echo from its own
transmission, since the transmit and receive lines are the same.
The IQ plus 800/810 has a built-in RS-485 software protocol, which
you enable by assigning an address to the EDP port on the CPU board.
From the setup menus, the progression is: SERIAL
DRESS, where the address is an ASCII decimal value other than zero.
We recommend addresses of 65 or higher.
Since the RS-485 protocol requires that each device has a unique
address, all remote commands are initiated as shown below:
<STX> <ADDRESS> <COMMAND> <CR>
ASCII 02
decimal
character
Address of the receiving
IQ plus 810 indicator.
If the initiating address matches the port address of an IQ plus
listening on the RS-485 network, that indicator responds.
800/810 uses 2-wire, you can incorporate other 4-
EDP serial command
ASCII carriage return character
NOTE: Host must send <CR>, not
<CR> <LF>. Failure to comply,
renders all indicators unable to
respond to serial commands.
EDP
AD-
®
800/810
Installation
2-9
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