Eprom U 5 0 5 ); Timer; Polled Controls - Welch Allyn Grason-Stadler GSI 17 Series Service Manual

once in each of 3 different blocks within the EEPROM.
calibration point is requested, the appropriate location in
of the three blocks is read and decoded.
valid the value
calibration error is detected, the frequency and transducer which
would use the data will not be available for testing by virtue of
channel being forced off.
the
function for all combinations of
which have valid calibration data.
even when power is not applied to the device.
The internal 256 bytes of RAM is used in a
capacity. It's
functions as adding HL dial to transducer RTL for a given
setting. This memory can only retain data when it
applied to it.
8.3

EPROM U 5 0 5 )

The K byte by
32
for the GSI
17.
and executes the instructions accordingly.
the Normal calibration and diagnostic modes are contained in this
EPROM is non-volatile memory, meaning that data
memory.
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
functions via 3 programmable outputs.
wave (SQWIN) which ultimately gets filtered into the pure tone
used for presentation into the earphones.
clock (SCFCLK)
points. These first two outputs (SQWIN, SCFCLK)
output frequencies dependent upon the
selected. The third output is a set pulse train which
negative-going
pulses are used as an interrupt for the processor so that it
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.
is, the CPU reads
determined rates of time.
at a rate of 12 msec.
status,
then if that control is determined to be in
status 12 msec later, it is acted upon.
stated
that the following controls are polled and allowed a de-
bounce time (settling time) every 12 msec.
as follows:
The HL Knob
The Frequency Dial
The =10 dB Extended Range Key
from 2 of the 3
used as a temporary storage
bit EPROM contains the operating
8
The microcomputer fetches data from
for setting the switched capacitor filter
.2 used pulse every
the status of
The polling in the GSI 17 takes
Every 12 msec a control is "looked at" for
For the data to be
blocks must
The instrument will
frequencies and transducers
This memory retains its
The instructions
One output is the
A second output is the
front panel
msec to
2
each key/control at
Therefore it
The keys/controls
When a
each
match. If a
continue to
data
"scratch-pad"
medium for such
output
has power
instructions
the EPROM
for
storage
different
square
3 dB
have variable
frequency
sends a
the CPU. These
can
That
pre-
place
the same
can be
are