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SERVICE INFORMATION
CLRADDR
r-l
NEXTADDR
LJ
I
CLK
IDDATA
I
Figure 4-9. IDDATA Timing Diagram
4.5.2 Switching
Circuitry
Matrix configuration
data is sent from the Model 707 via
the RELAY DATA control line and serially loaded into the
I2 shift registers (U3Cl through U41). The matrix card relays
configure
accordingly
when
the registers
receive the
STROBE signal from the Model 707 A relay is energized
when a register output
is low (connected to digital com-
mon). A register output is low
when
a "high"
data bit is
clocked into it (i.e. inverting
drivers).
4.5.3 Power Up Safeguard
To prevent relays from inadvertantly
energizing
and caus-
ing possible damage during power up, a safeguard circuit
has been incorporated
into the design. The protection cir-
cuit is comprised
of a dual NAND
gate (U42) and an RC
network (Rl, C20 and CRI). The time constant of the RC
network keeps the the output of the NAND gate high dur-
ing the power up sequence. This high signal is applied to
the OEN input of the shift registers keeping the relays
de-
energized. After the capacitor of the RC network charges,
a STROBE signal will then force the output of the NAND
gate low allowing
configured
relays to energize.
4.6 SPECIAL
HANDLING
OF STATIC-
SENSITIVE
DEVICES
CMOS and other high-impedance
devices are subject to
possible
static discharge
damage because of the high-
impedance levels involved. The following
precautions per-
tain specifically
to static-sensitive
devices. However, since
many devices in the Model 7U7l are static-sensitive,
it is
recommended
that they all be treated as static-sensitive.
1. Such devices should be transported
and handled only
in containers specially designed to prevent or dissipate
static build-up.
Typically,
these
devices will be received
in anti-static containers
made of plastic or foam. Keep
these parts in their original
containers
until ready for
i"stalIatio".
2. Revove the devices from their protective containers only
at a properly
grounded
work station.
Also ground
yourself with a suitable wrist strap while working with
these devices.
3. Handle the devices only by the body; do not touch the
pins.
4. Any printed circuit board into which the device is to be
inserted must first be grounded
to the bench or table.
5. Use only
anti-static
type
de-soldering
tools
and
grounded-tip
soldering
irons.
414
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