Welch Allyn GSI 38, Service Manual

Page: 31 / 96

Monitoring of the Switch Matrix Keys Continued:
The present bar, subject response switch, frequency up/down key, paper advance key,
and page key all function as press and hold controls where the corresponding function
is active only as long as the control is pressed. Single action controls include the mode
control keys (Prog, Aud, Tymp, Tymp/Reflex) tone type keys (FM, Steady, Pulsed),
routing keys (L,R), memory control keys (Page, M-, M-), and the printer control keys
(Print Screen, Print All, Paper Advance).
Normal/Calibration Mode Switch: The slide switch is monitored by the processor thru
the switch input buffer U31. It is utilized for entry to the calibration and diagnostic
modes.
Dip Switches: Dip switches 1 thru 4 are connected directly to the microprocessor A/D
convertor. Dip switches 5 thru 8 are connected to the switch input buffer U31. These
dip switch selections are read or processed upon entry to the calibration mode. When
calibration mode is selected the dip switch status is verified and processed according
to the individual selections. Any change in the dip switch status after entry to the
calibration mode will be ignored by the processor.
Hearing Level Control (HL): The hearing level control dial is connected to a 36
position 2 bit encoder (RE1) located on the HL Board. The encoder output from the HL
board is connected to port A of the audio processor. In the audiometer mode this
rotary knob selects the stimulus hearing level based on the relative position change of
the knob from the previous hearing level selection.