Studio Technologies ISS - Manual (Page 29)

Issue 3, June 1990 ISS User Guide
Page 30 Studio Technologies, Inc.
ISS
the source of the remote control signals
and the ISS circuitry. A resistor in series
with the optocoupler photodiode provides
current limiting to protect the remote control
signal source and the photodiode. A diode
is connected anode to cathode/cathode to
anode across the photodiode to prevent a
polarity reversal on the remote control
signal from damaging the optocoupler.
The optocoupler output signals are buffered
using inverting Schmidt trigger logic buff-
ers. The output of the buffer is now truly a
“clean” logic signal. This logic signal di-
rectly follows the remote control input. A
feature of the ISS is that continuous or
pulse remote control signals can be inter-
faced. To accommodate this, a four pole
switch selects whether the ISS will respond
to continuous or pulse signals. In the con-
tinuous mode, the output of the Schmidt
inverting buffer is sent directly to the next
section of circuitry. In the pulse mode, the
output of a D flip-flop, whose input is from
the Schmidt inverting buffer, is connected to
the next section of circuitry. The four signals
from the remote control inputs go to differ-
ent paths.
The Remote I/O Bypass signal drives the
base of NPN transistor Q1. Q1 is connected
to the ribbon cable bus in an open collector
configuration. The I/O Card uses this signal
to control its I/O Bypass control circuit.
Notice that the reset pin of the Remote I/O
Bypass flip-flop is connected to one section
of the inverting Schmidt trigger acting as a
power-up reset circuit. This power-up reset
circuit insures that upon power-up the flip-
flop starts in the desired state.
The signal from Remote Control Enable is
active only when the mode select switch is
in the AUTO + REMOTE position. A tricky
arrangement is used to provide power-up
reset and a circuit active signal using a
Schmidt trigger inverting buffer. When in
the AUTO + REMOTE mode, the remote
enable signal connects to three places:
selector pin B of U8, the ribbon cable bus
as the IMMEDIATE signal, and to a buffer
acting as an LED driver. When the remote
enable signal is high, U8 selector pin B
goes high, selecting the signals on pins X2
and Y2 to go to the outputs. This lets the
Remote Sim L and Remote Sim R control
the Crossfade Card. The remote enable
command is buffered and sent to the
Crossfade Card as the IMMEDIATE com-
mand. (This triggers the Remote Control
Enabled relay and changes the crossfade
speed to immediate.) The remote enable
signal also causes the Remote Enabled
LED to light on the front edge of the Mode
Select Card.
The Remote Sim L and Remote Sim R
signals have a set of NAND gates (U11)
associated with them to insure that only
one can be selected at a time.
Crossfade Card
The Crossfade Card contains two major
sections: audio control and logic control.
Audio Control: The audio inputs to the
Crossfade Card are selected via the three
position INPUT switch. These three input
sources are connected to the Crossfade
Card via the ribbon cable bus. The switch
chooses the input source: signals from the
I/O Card, the Polarity Correction Card, or
the optional Tone Detection Card. The
switch selected audio inputs connect to
two points in the circuit: analog switch U9
and voltage controlled amplifier (VCA)