SAE 800
Circuit Description
Trigger
Positive pulses on inputs E1 and/or E2 trigger the IC. The hold feedback in the logic has a delay of
several milliseconds. After this delay has elapsed, the tone sequence is started. This prevents
parasitic spikes from producing any effect on the trigger pins.
The following table shows the trigger options:
E1
E2
Mode
Issued Sequence
Minor and major third
Minor third
Triggered
Grounded/open
Triggered
Triggered
Triggered
Grounded/open
Triple-tone
Dual-tone
Single-tone
1st tone of minor third
Oscillator
This is a precision triangle oscillator with an external time constant (R x C). Capacitor CC on pin COSC
is charged by constant current to 1 V and then discharged to 0.5 V. The constant current is obtained
on pin ROSC with an external resistor RR to ground.
When the voltage on COSC is building up, the logic is reset at 350 mV. This always ensures that a
complete tone sequence is issued. If the oscillator pin is short-circuited to GND during operation,
the sequence is repeated.
The following applies:
∆VC x CC = IC x T/2 with IC = VR/2RR = 1.2 V/2RR
f0 = 5/8 x 1/(RR x CC)
Voltages on Pin COSC
Semiconductor Group
4
SIEMENS [ Siemens Semiconductor Group ]
