Amplicon Magic 485F25 Manuale di istruzioni - Pagina 8

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2.4

Configurable Options

Selection of DCE or DTE (485F25 only)

The unit, as supplied from the factory, is configured to interface directly to a DTE i.e. a PC or

dumb terminal . In the majority of applications this will be correct. This is set by the Jumpers J1

to J2. If required the unit can be converted to connect to a DCE e.g. a moedm, by the

repositioning of J1 and J2, as detailed below.

Link

J1 1-2 & J2 1-2

J1,1- J2,1 & J1,2 - J2,2

Selection of Local Echo On/Off in Half Duplex Operation

The factory default configuration of link (J3) fitted causes the transmitted data to be echoed to

the receiver in half duplex operation. If this echo is not required, the link can be removed.

For full duplex operation, the link J3 must be in its default condition for the receiver to be

continuously enabled. Echo back is not appropriate to full duplex operation.

Link

485F25

485F9

J3 1-2

J3 linked

J3 2-3

J3 cut

Transmission Line Termination

For proper operation of the RS422/485 bus in full or half duplex, multi-drop or point-to-point

communication, it is recommended that termination be applied to the receiver end of the data

lines. The simplest form of termination is line-to-line with typically a 120 Ω resistor across the

differential input.

In a multi-drop system, the terminator resistor is only required at the device receiver located at

the far end of the cable. If this is in half duplex operation, then both ends of the bus cable are

equipped with receivers (transceivers) so termination is necessary at both ends. Although the

Magic 485F Adapter will drive loads as low as 27 Ω, in general, RS485 transmitter circuits are

specified as being capable of driving a minimum load resistance of 60 Ω, so no more than two

terminator resistors should be connected to any one bus.

The Magic 485F Adapter is equipped with a terminator resistor for the receiver input pair. This

resistor is connected into circuit by the setting of switch SW1 Bit 4 on the 485F25 or solder link

J1 on the 485F9. Factory default settings are with the receiver input termination in circuit (SW1-

4, on) for the 485F25, and (J1 solder link tracked) for the 485F9. It can be removed from the

circuit by setting SW1-4 to off on the 485F25 or cutting the fine track connecting the pads of J1

on the 485F9.

Page

Function

RS232 connector wired as PC serial port (default factory setting)

RS232 connector wired as Modem serial port

Function

RS485 local echo disabled (default factory setting)

RS485 local echo enabled, transmitted character echoed back to

receiver

Magic 485F Adapter