Technical Description
Sealevel Systems
ISO-16
Page
5
Technical Description
The
ISO-16
provides four parallel input/output (I/O) ports. The ports are
organized as ports A, B, C, and D. Port A and B are the input ports and are
interfaced to optically- isolated inputs, while ports C and D unused. Assuming
an I/O address of 300 Hex the following table shows the Port Addresses.
Base Address
Hex
Decimal
Mode
Port A Address
300
768
Input Port (Opto Input)
Port B Address
301
769
Input Port (Opto Input)
Port C Address
302
770
Unused
Port D Address
303
771
Unused
Features
•
Selectable I/O port addressing from 100H - 3FFH
•
2 eight bit input ports
•
DB-37 female connector for optically isolated inputs
•
8 bit slot connector
•
Multiple adapters can reside in same computer
•
All address, data and control signals are TTL compatible
Ports A and B are 8 bit-input ports connected to optically isolated input
sensors. Each sensor can be used to interface a voltage input and then sense
whether the voltage is on or off. Each sensor is isolated (with respect to a
common ground) from every other sensor, and also isolated with respect to the
host PC ground. This means that signals such as low-level AC line voltage,
motor servo voltage, and control relay signals can be ‘sensed’, or read by the
PC, without the risk of damage due to ground loops or ground faults.
Each sensor-input pair has a current limiting resistor, which is used to limit the
input current to the opto-isolator. The opto-isolator has two ‘back-to-back’
diodes internally. This allows AC or DC signals to be sensed, regardless of
polarity. When the applied voltage is high enough to cause the led in the
opto-isolator to turn-on, the output of the opto-isolator goes low (0 volts) and
the signal is read as a low logic level (binary 0) by the PC. When the input
signal is too low to turn on the opto-isolator, the output goes high and the port
bit is read by the PC as a high logic level (binary 1).
