MSAN-101 Zarlink Semiconductor, Inc., MSAN-101 Datasheet - Page 10

• Manufacturer Part Number: MSAN-101
• Description: Applications of the MT8804A 8 x 4 Analog Switch Array
• Manufacturer: Zarlink Semiconductor, Inc.

MSAN-101
‘DISCONNECT’ button. Pressing the ‘MASTER
RESET’ switch at any time disconnects all test
instruments from all test points.
Circuit Operation
The two MT8804A’s are the heart of this analog
switching circuit, coupling combinations of test
instruments to the eight test points of the circuit
under test. Using all CMOS components and
asynchronous operation results in ultra-low operating
power consumption.
The allowable voltage swing from the signal sources
is from +5V to -5V as determined by the MT8804A
power supplies. The control inputs swing from +5V to
0V. User control of the circuit is via a standard 16
switch keypad and four additional momentary push-
button switches. The keypad consists of 16 SPST
switches with one common terminal which is
connected to V
‘1’ through ‘8’ are connected to an 8 line to 3 bit
binary encoder (4532). The remaining keys are
connected to NOR R-S latches (4043) directly. All
sixteen switches are pulled to ground through
resistors.
Pressing the ‘TEST POINT’ switch clears all the
latches, setting up the circuit for new data. The
address (A
encoder is asynchronously latched. This address is
decoded by the MT8804A to select the line (L
A-26
0
, A
1
DD
, A
= +5V. The eight switches, marked
2
) of the MT8804A from the ‘4532’
Figure 9 - 4-Channel 4-Bit D/A Converter
0
- L
7
)
and hence the test point corresponding to the
numbered key pressed. The Group Select (GS)
output of the ‘4532’ goes high whenever one of its
eight data inputs goes high. This signal is also
latched and used to gate the AE pulse to the
MT8804A. This ensures that a test point number has
been entered and hence prevents unwanted or
accidental connections. A series of designated test
equipment keys is pressed setting corresponding
latches which are connected to the data inputs (D
D
These data inputs in turn correspond to the junctors
(J
Pushing the ‘CONNECT’ button pulses the AE inputs
of the two MT8804A’s, completing the desired
connection.
During a disconnect sequence, the latches are
cleared by the ‘TEST POINT’ switch. The numbered
key pressed sets up the address of the test point to
be disconnected. Pressing the ‘DISCONNECT’
button next pulses the AE inputs. However, this time,
all data inputs are at logical 0’s so that all switches to
the addressed test point are opened. The ‘MASTER
RESET’ when activated opens all switches in the
MT8804A disconnecting all test equipment from all
test points. A power-up reset is provided by the
resistor, capacitor and inverter in the master reset
line. This prevents unwanted connections on power-
up. Any convenient values of resistance and
capacitance are appropriate provided that the power-
up time is short in comparison to the time constraint.
3
0
) of the MT8804A’s.
- J
3
) to which the test equipment is connected.
0
-