D-Asic Pwm Signals - Fluke ScopeMeter 123 Service Manual

The keys are arranged in a 6 rows x 6 columns matrix. If a key is pressed, the D-ASIC
drives the rows, and senses the columns. The ON/OFF key is not included in the matrix.
This key toggles a flip-flop in the D-ASIC via the ONKEY line (D-ASIC pin 72). As the
D-ASIC is permanently powered, the flip-flop can signal the test tool on/off status.
PWM Signals
The D-ASIC generates various pulse signals, by switching a reference voltage
(REFPWM1 or REFPWM2), with software controllable duty cycle (PWMA, PWMB
pins 26-40). By filtering the pulses in low pass filters (RC), software controlled DC
voltages are generated. The voltages are used for various control purposes, as shown in
Table 3-6.
PWM signal Function
HO-RNDM HOLDOFF randomize control
TRGLEV1D, Trigger level control
TRIGLEV2D
POS-AD, POS-BD Channel A,B position control
OFFSETAD, Channel A,B offset control
OFFSETBD
BACKBRIG Back light brightness control
CONTR-D Display contrast control
SADCLEVD S ADC comparator voltage
CHARCURD Battery charge current control
Table 3-6. D-ASIC PWM Signals
Destination
R487 of RANDOMIZE circuit
T-ASIC
C-ASIC
C-ASIC
Back light converter (POWER part)
LCD unit
SLOW ADC (POWER part)
P-ASIC
Circuit Descriptions
3.3 Detailed Circuit Descriptions
Reference
REFPWM1
REFPWM1
REFPWM1
REFPWM1
REFPWM1
REFPWM1
REFPWM2
REFPWM2
3
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