2-35
2
2.12
EXAMPLE I/O CONNECTIONS
Figure 2-12 shows how a 4807 may be used to control various devices in a
chassis and input data. In Figure 2-12, the host chassis has some push-
button inputs that have to be sensed, a small Digital Panel Meter (DPM), an
LED display, a motor controlled by analog voltages, and a relay. The 4807's
A/D measures the feedback wiper position and the temperature of the
amplifier and motor. Figure 2-12 shows some ways that data can be
transferred to or from the external device and the GPIB bus or Serial port.
Table 2-11 shows the signal connections for this example. Table 2-12
shows the corresponding configuration settings.
The first Digital I/O byte is used as inputs so the push-button can be
monitored by the 4807's Questionable Event Register. The Status Reporting
Structure is enabled to generate a Service Request anytime the push-button
is pressed. The byte may also be directly queried with the
PORTn?
query
to read any static signals or to test the push-button.
Bytes 2 and 3 are used to input data from a 2 1/2 Digital Panel Meter (DPM)
data as a four character ASCII string. The string is read with the
PORT?
(@2,3)
query. Typical in-range responses are -199 to + 199. The
Overrange signal is wired to bit 8 of the 100s digit so Overrange responses
are -999 or +999. The polarity digit is created by wiring the plus polarity
signal to bit 1 and jumpering bits 8, 4 and 2 to ground. The resulting reading
is >1000 for negative numbers. The reading can be tested and changed to
a negative number in the computer.
i.e.
IF Reading > 1000 THEN
Reading = (Reading -1000) * -1
END IF
Byte 4 is used to control the LED display. If the Display has its own
memory, a spare Relay Driver output line could be used to strobe the data
into the Display's memory. (Use a pullup resistor to convert the open
collector relay driver outputs to a TTL compatible signal.) Use the
SOURCe:DATA:PORT4
command or the short form
BO4
command to
update the LEDs. Use
ROUT:CLOSE 1; ROUT:OPEN 1
to pulse the
relay driver output.
One of the D/A outputs drives an amplifier to control the motor. The power
relay turns the motor off when it is not being used. (A suppression diode
