Chapter 3: OPTION SELECTION
To help you locate the jumpers described in this section, refer to the OPTION SELECTION MAP at the end of
this section. Operation of the serial communications section is determined by jumper installation as described
in the following paragraphs.
120
S
TERM
TERMINATIONS:
A transmission line should be terminated at the receiving end in its characteristic impedance. Installing a
jumper at the location labeled TERM applies a 120
Ω
load across the transmit/receive input/output for RS-485
operation.
In RS-485 operations where there are multiple terminals, only the RS-485 ports at each end of the network
should have terminating resistors as described above. Also, for RS-485 operation, there must be a bias on the
RX+ and RX- lines.
If the board is not to provide that bias, contact the factory technical support.
DATA CABLE WIRING
INTERRUPTS:
The board supports IRQ 2, 3, 5, 7, 10 and 11 (unless reserved by other installed hardware).
The levels are selected by writing the desired IRQ level to the appropriate address in the EEPROM and having
it (them) loaded from the EEPROM into the appropriate registers. Channels A, B, C and D have individual
interrupts and channels E, F, G and H share a fifth interrupt. It is necessary to load interrupt values for all of the
channels. If the same interrupt is to be used for all channels, it must be entered into all five of the interrupt
locations in the EEPROM.
Please note: In Windows NT, changes must be made to the System Registry to support IRQ sharing. The
following is excerpted from “Controlling Multiport Serial I/O Boards” provided by Microsoft in the MSDN
library.Document id: mk:@ivt:nt40res/D15/S55FC.HTM, also available in the Windows NT Resource Kit. The
text enclosed in brackets (“[]”) denotes a comment.
The Microsoft serial driver can be used to control many
dumb
multiport serial boards.
Dumb
indicates that the
control includes no on-board processor. Each port of a multiport board has a separate subkey under the
CurrentControlSet\Services\Serial subkey in the Registry. In each of these subkeys, you must add values for
DosDevices
,
Interrupt
,
InterruptStatus
,
Port Address
, and
PortIndex
because these are not detected by
the Hardware Recognizer. (For descriptions and ranges for these values, see Regentry.hlp, the Registry help
file on the
Windows NT Workstation Resource Kit CD
.)
Manual 104-COM-8S
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