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Why use an ISP?
The answer to the polling inefficiency was the Interrupt Status Port (ISP). The ISP is a read only 8-bit register
that sets a corresponding bit when an interrupt is pending. Port 1 interrupt line corresponds with Bit D0 of
the status port, Port 2 with D1 etc. The use of this port means that the software designer now only has to
poll a single port to determine if an interrupt is pending.
The ISP is at Base+7 on each port (Example: Base = 280 Hex, Status Port = 287, 28F... etc.). The ULTRA
COMM+422.PCI will allow any one of the available locations to be read to obtain the value in the status
register. Both status ports on the ULTRA COMM+422.PCI are identical, so any one can be read.
Example: This indicates that Channel 2 has an interrupt pending.
Connector Pin Assignments
RS-422/485 (DB-9 Male)
DB-37 Connector Pin Assignments
© Sealevel Systems, Inc.
7402 Manual | SL9063 7/2021
Bit Position:
7
6
Value Read:
0
0
Signal
Name
GND
Ground
TX +
Transmit Data Positive
TX-
Transmit Data Negative
RTS+
Request To Send Positive
RTS-
Request To Send Negative
RX+
Receive Data Positive
RX-
Receive Data Negative
CTS+
Clear To Send Positive
CTS-
Clear To Send Negative
Port #
1
2
GND
33
14
TX-
35
12
RTS-
17
30
TX+
34
13
RX-
36
11
CTS-
16
31
RTS+
18
29
RX+
37
10
CTS+
15
32
5
4
3
2
1
0
0
0
0
0
1
0
Pin #
Mode
5
4
Output
3
Output
6
Output
7
Output
1
Input
2
Input
9
Input
8
Input
3
4
24
5
26
3
8
21
25
4
27
2
7
22
9
20
28
1
6
23
18
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