Omega Vehicle Security OMG-ULTRACOMM2-PCI RS-232 - Manual (Page 16)

Technical Description
Omega Engineering OMG-ULTRA COMM+2.PCI Page 12
software designer with a challenge to identify the source of the interrupt. The
software designer frequently used a technique referred to as ‘round robin
polling’. This method required the interrupt service routine to ‘poll’ or interrogate
each UART as to its interrupt pending status. This method of polling was
sufficient for use with slower speed communications, but as modems increased
their through put abilities this method of servicing shared IRQs became
inefficient.
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 soft ware 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 OMG-ULTRA COMM+2.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 OMG-ULTRA COMM+2.PCI are identical, so any one can be read.
Example: This indicates that Channel 2 has an interrupt pending.
Bit Position: 7 6 5 4 3 2 1 0
Value Read: 0 0 0 0 0 0 1 0
Connector Pin Assignments
RS-232
Name Pin # Mode
TD Transmit Data 3 Output
RTS Request To Send 7 Output
DTR Data Term Ready 4 Output
GND Ground 5
RD Receive Data 2 Input
DCD Data Carrier Detect 1 Input
DSR Data Set Ready 6 Input
CTS Clear To Send 8 Input
RI Ring Indicator 9 Input
Note: These assignments meet EIA/TIA/ANSI-574 DTE for DB-9 type
connectors.