Introduction; Figure 1: Model 8020-38 Addressable Bus Converter - Geokon 8020-38 Instruction Manual

1.

INTRODUCTION

The Model 8020-38 Addressable Bus Converter enables connections
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between addressable sensor strings and a variety of systems, including
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personal computers, programmable logic controllers, readouts, and data
loggers.
The Addressable Bus Converter acts as a bridge between USB- or TTL-capable
readers and the RS-485-enabled sensor strings. The device supports
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bidirectional signal conversion between USB and RS-485 or between TTL and
RS-485.
The Converter draws its power from the 5 volt USB bus when connected to a
computer via the USB port. It then generates its own 12 volt supply for the RS-
485 bus, which is used to power the sensor string. The Converter requires an
external 12 volt, 500 milliamp DC power supply when connected via a TTL port.
In the case that the Converter is connected to both USB and TTL simultaneously,
the USB host is selected by default.
The Converter can communicate with the host over USB version 1.0 and higher,
over 5-volt TTL, and/or over inverted 5-volt TTL. If the host requires TTL inversion
the 'INV TTL' switch on the underside of the PCB must be set to the ON position.
See Section 2.3 for more information.
Communication with addressable sensor strings uses the MODBUS
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RTU protocol over a half-duplex RS-485 connection. The Converter is designed
for addressable string systems and features resettable baud rates,
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ranging between 9600 bits per second and 115.2 kilobits per second.
The Converter is contained inside a rugged ABS plastic case and incorporates a
variety of safety features. These include high current surge protection, transient
voltage suppression, electro-static discharge protection, and a heavy-duty earth
ground lug.
Ground Lug
TTL Spring
Terminal
RS-485 Spring
Terminal
USB Port

FIGURE 1: Model 8020-38 Addressable Bus Converter

MODEL 8020-38 ADDRESSABLE BUS CONVERTER | INTRODUCTION | 1