B&B Electronics MAP450D installation manual OIT #2

INSTALLATION MANUAL 11

There are several different forms of communications networks. Maple Systems’ OITs utilize the multidrop format. The host controller, located at one of the network ends, is connected to the OITs via a continuous com-link. Each OIT is connected to the network by locally tapping into the com-link with short stub cables. The end of the com-link must be properly terminated to reduce noise pickup and interference. The total length of the com-link, from the host controller to the network cable terminator, can be up to 4,000 feet.

HOST	See
	Detail A & B
	TERMINATOR

Less than

4000'

Less than 12" Shielded Cable

TERMINATOR

OIT #1

2 Pair Twisted
Shielded Cable
24 Gage Wire
From Host or
Previous OIT
Drain	CHASSISGND	RXD+/TXD+	RXD-/TXD-	SIGGND	SIGGND
Wires
	CHASSIS GND	RXD+ TXD+	RXD- TXD-	SIGGND

OIT #2

From Host or

Previous OIT

To More

OITs

Drain

Wires

OIT #100 3 Pair Twisted

Shielded Cable

24 Gage Wire

To More

OITs

CHASSISGND TXD+ TXD- RXD+ RXD- SIGGND SIGGND

TO OIT	TO OIT
Detail A	Detail B
5 Wire Termination	5 Wire Termination

If you decide to use 3-wire RS-422/485, the following limitations apply:

•The host controller must disable or tri-state its RS-485 transmitter when it is not sending data to the OITs on the network. To simplify programming, the host should disable or tri-state its RS-485 receiver whenever transmitting.

•The ability to stay logged on to a particular OIT by sending the command terminator instead of the line terminator is not available in this mode. Therefore, each command sent from the host controller should end with the appropriate line terminator.

•If the host controller sends a command that requires a response from the OIT, the host controller must wait for a response from the OIT before sending another command. Otherwise, a situation can occur in which the OIT and the host controller attempt to transmit at the same time cuasing unpredictable results.

•The ASCII strings sent by the OIT’s function keys should not include any control characters which the other OITs on the network could misinterpret, such as the line terminator or command terminator.

1010-0046A, REV 00