Amplicon Magic 485F25 Руководство по эксплуатации - Страница 3

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INTRODUCTION

1.1

General Description

The Magic 485F 'MAGIC converter' transfers data between RS232 & RS485 networks. The unit

is 'magic' in that, unlike conventional converters, it does not require the RTS signal to control

RS485 transmitter turnaround. Instead the RS485 transmitter is enabled whenever a valid start

bit is detected on the RS232 input. This feature can be very useful when connecting RS232

based modems, or other systems that do not support RTS handshaking to RS485 multidrop

networks.

The data conversion process changes only electrical levels and the pin-out configuration is in

accordance with the appropriate standards. As default the unit is supplied for the RS232 host

device configured as Data Terminal Equipment (DTE) but can be changed by jumpers to a Data

Communication Equipment (DCE).

RS485 multi-drop operation allows up to 32 devices to be connected in a simple network on a

single serial bus. The transmitter has a tri-state output and is automatically disabled to allow

reception over the same wire pair.

DC power for the Magic 485F Adapter must be applied from an external source. The DC power

lines plus the RS422/485 data and control signals are connected through a pluggable 8 way

screw terminal assembly at the free end of the Adapter.

1.2

The Products Described in this Manual

The 485F range of boards share some common circuitry and features and are referred to in this

manual either generically or individually:

485F

485F25

485F9

1.3

Circuit Operation

The Magic 485F Adapter converts the electrical levels of signals from those specified for RS232

to the RS422/485 levels and vice versa. This conversion is done via intermediate TTL levels.

RS232 <–––> TTL

U2 is a MAX2322E (or equivalent) 5 V powered CMOS RS232 Driver/Receiver. A DC-DC

converter is built into the chip to provide a typical ±9 V output swing of the RS232 lines.

This receiver accepts signal at RS232 levels and converts these signals to TTL levels for

internal use. The first receiver accepts the transmitted data (TxD) signal from the RS232 port

and translates it to TTL levels for onward conversion by the RS422/485 driver.

This line is then fed to a FPGA device, U4, which monitors the data coming into the unit. If

the unit detects a valid start bit, the device enables the transmitter and disables the

receiver of the MAX491 transceiver chip U1. Once the packet of data is transmitted and

the turnaround time has passed, as set by SW1, the unit reverts to receive mode.

MAGIC 485F

Refers to both boards

Refers to the 25 way D-type version only

Refers to the 9 way D-type version only

Magic 485F Adapter

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