once in
each of 3 different blocks within the EEPROM.
When a
calibration point is requested,
the appropriate location in
each
of the
three blocks is read and decoded.
For the data to be
valid
the
value
from 2 of the 3 blocks must
match.
If a
-
calibration error is detected,
the frequency and transducer which
would use the data will not be available for testing by virtue of
the
channel being forced off.
The instrument will
continue to
function for
all combinations of
frequencies and transducers
which have valid calibration data.
This memory retains its
data
even when power is not applied to the device.
The
internal 256 bytes of RAM is used in a
"scratch-pad"
capacity.
It's
used
as a temporary storage
medium for
such
functions as adding HL dial to transducer RTL for a given
output
setting.
This memory can only retain data when it
has power
applied to it.
8.3 EPROM
U505)
The
32
K byte by
8
bit EPROM contains the operating
instructions
for
the GSI
17.
The microcomputer fetches data from
the
EPROM
and executes the instructions accordingly.
The instructions
for
the Normal calibration and diagnostic modes are contained in this
memory.
EPROM is non-volatile memory, meaning that data
storage
is not lost when power is removed from the device.
8.4 TIMER
(U511)
There is a programmable timer chip which is used for 3
different
functions
via 3 programmable outputs.
One output is the
square
wave (SQWIN) which ultimately gets filtered into the pure tone
used for presentation into the earphones.
A second output is the
clock (SCFCLK)
for setting the switched capacitor filter
3
dB
points.
These first two outputs (SQWIN, SCFCLK)
have
variable
output
frequencies dependent upon the
front panel
frequency
selected.
The third output is a set pulse train which
sends a
negative-going
.2
used pulse every 2
msec
to
the CPU.
These
pulses are used as an interrupt for the processor so that it
can
update
the COP circuit and perform the polling of the status of
the controls not previously mentioned.
8.5 POLLED CONTROLS
The majority of controls are read via a polling technique.
That
is,
the
CPU reads
the status of
each
key/control at
pre-
determined rates of time.
The polling in the GSI 17 takes
place
at a rate of 12 msec.
Every 12
msec
a control is "looked
at"
for
status,
then
if that control is determined to be in
the same
status
12
msec
later,
it is acted upon.
Therefore it
can be
stated
that the following controls are polled and allowed a
de-
bounce time (settling time) every 12 msec.
The keys/controls
are
as follows:
The HL Knob
The Frequency Dial
The
=10
dB
Extended Range Key
-
62
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