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The
clock
controller (Ie U44 on the logic B PCA) is a National Semiconductor NS58167 A IC that
counts from 1/10,000 second to months. It contains two interrupt outputs. The STANDBY INT output
interrupts at interrupt level 6 when the clock count matches a predetermined value (user
programma-
ble). The
INT
output interrupts at interrupt level 1 either when a predetermined value is matched or at
a predetermined periodic interval (also user programmable).
The 32.768-kHz oscillator (Yl on the logic B PCA) can be fine tuned by adjusting the variable capac-
itor (C43
on
the logic B
PCA)
connected to pin 10 of the controller Ie.
The oscillator is connected to an LM 358 operational amplifier (U40
~n
the logic B peA). The opera-
tional amplifier is wired in voltage-follower configuration to buffer the clock signal. The buffered
dock signal
is available at test point
TPl for measurement with a frequency counter.
The standby lithium battery (BTl on the logic B PCA) maintains clock operation while the computer is
turned off. The battery has a six-year
minimum expected life (12 years typical).
Each of the controller address and control lines is connected to ground through a 22-kO resistor (R38
on the logic B peA). This prevents the inputs from floating into their linear operating regions when
the computer is turned off, reducing the drain on the standby battery.
5.14 Speaker
The speaker
(LSI
on the logic
B
PCA) allows the user to generate tones in the range 100
Hz
to 5000
Hz.
The speaker controller (Ie U39 on the logic B peA) is a National Semiconductor COP 452 frequency
generator/counter. The controller outputs a square wave, the frequency and number of pulses of
which are programmable.
5.15 HP-IB Interface
The computer contains an HP·IB (Hewlett-Packard Interface Bus) interface that is compatible with the
1EEE-488 standard. It
is the primary
means for interfacing the computer to peripherals such as plot-
ters, external printers, and external disc drives. The HP-IB interface is also often used for data
acquisition and controller applications.
The interface circuit includes two
bus
transceivers: an SN 75160A (Ie U42) and an SN 75162A (Ie
U43). It also includes a 9914 talker/listener/controller Ie (IC U41). An ALSOO quad-NAND IC (Ie
U26) provides for the decoding of the controller:enable signal. All of these components are located on
the logic B PCA.
Jumper
WI
defines whether the interface is to
be
system controller of the
HP-IB
or not. It is fadory set
in the system controller position since the interface is most often
used
in this mode.
All bus configuration is done by the operating system at initialization or by the application program.
Therefore, no switches are required
fo~
this purpose.
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