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Card Setup
Address and IRQ selection
The SIO4-104.485 is automatically assigned I/O addresses and IRQs by your
motherboard BIOS. Only the I/O address may be modified by the user. Adding or
removing other hardware may change the assignment of I/O addresses and IRQs.
Electrical Interface Selection
The SIO-485.LPCI can be individually configured via SW1 as RS-422, or as a
two/four wire RS-485 interface. The following table illustrates the electrical modes
for SW1:
Electrical Mode
RS-422
RS-485 4 Wire
RS-485 2 Wire
Line Termination
Typically, each end of the RS-485 bus must have line-terminating resistors (RS-422
terminates at the receive end only). A 120-ohm resistor is across the RS-422/485 data
input in addition to a 1K-ohm pull-up/pull-down combination that biases the receiver
inputs. The 120-Ohm termination is 'switched' in or out by SW1 (silk screen position
'T'). With the switch in the 'On' position, termination is present. With it in the 'Off'
position termination is removed.
RS-485 'Echo'
The RS-485 'Echo' is the result of connecting the receiver inputs to the transmitter
outputs. Every time a character is transmitted; it is also received. The SIO-485.LPCI
automatically suppresses this 'Echo'.
Clock Modes
The SIO-485.LPCI utilizes a 14.7456 MHz oscillator. This is eight times faster than
the standard COM: port oscillator, which typically is 1.8432 MHz. This allows the
adapter to achieve a maximum data rate of 921.6Kbps. The following sections outline
the baud rate calculations and instructions for achieving your desired baud rate.
© Sealevel Systems, Inc.
Switch Position 1
Switch Position 2
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On
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SIO-485.LPCI User Manual
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