User`s manual

Chapter 1
Introducing the CYCOM 485
The CYCOM 485 is a serial interface for the IBM PC and compatibles. The UART (serial communications
chip) is a 16550. The physical interface conforms to the RS485 standard.
The 16550 UART is the standard UART of the personal computer. Any software which is designed to control
IBM PC serial COM ports will work with the C
YCOM 485. A base address switch and interrupt jumper allow
you to select one of four COM ports; COM1, COM2, COM3, or COM4.
The RS485 interface allows multiple transmitters as well as multiple receivers to communicate on a two-wire
serial link thereby making possible serial networks. Many instruments are equipped with RS485 interfaces as
are the remote data acquisition and control modules from CyberResearch, Inc.
Because the RS485 interface calls for each node to be either a transmitter or receiver, the C
YCOM 485 can
swap the transmit and receive lines. A register on the board allows you to set the C
YCOM 485 as a transmitter
or receiver. Once written to, this register is not overwritten by standard COM software. The power on default is
to configure the C
YCOM 485 with neither the transmitter or receiver enabled. One or the other must be enabled
via program control.
RS485 is a step up from RS422. RS422 allows multiple receivers but only one transmitter.
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