Emergency; Mechanical On/Off - Motorola MCS 2000 Service Instructions Manual

Controller Section Theory of Operation: Voltage Regulation

Emergency

(Refer to schematic Page 10-30 for reference)
The emergency switch, when not engaged, normally grounds the base of Q0414. When the
emergency switch is pressed this connection is opened and the base of Q0414 is pulled high by
R0437. This causes the collector of transistor Q0414 to go low (.2V), thereby setting the
EMERGENCY IN input of U0510 low. U0510 is a dual 555 timer configured as two "pulse stretchers",
one for the Emergency input to electronically turn on the radio and the other for the mechanical On/
Off switch on the control head to cause the radio to electronically switch on.
With regard to emergency, when U0510-8 EMERGENCY IN is above 1/3 of the supply voltage at
U0510-14, that causes the device to internally ground U0510-13, which in turn holds capacitor
C0513 in a discharged state. The device also keeps U0510-9 EMER TRIG at a low voltage. When
EMERGENCY IN goes below 1/3 of the device supply voltage, U0510 disables the discharge
mechanism at pin 13 allowing the capacitor C0513 to charge through R0513. The charging rate is
set by the values of R0513 and C0513. When the voltage at pin 12 goes above 2/3 supply voltage,
the device sets pin 9 EMER TRIG high which in turn switches on Q0510 enabling the radio to turn on
to begin emergency operation. U0510 will keep pin 12 high for a period set by R0513 and C0513
which for 200K/1 uF equals 220 ms.
While SW B+ is on for 220 ms, the microprocessor starts execution, reads that the emergency input
is active, and sets the B+ CNTL output to a logic high. This high will keep Q0510 switched on
through CR0510 beyond the 220 ms period after which U0510-9 will return to a low level. This
operation allows a momentary press of the emergency switch to power up the radio. When the
microprocessor has finished processing the emergency press, it sets the B+ CNTL output to a logic
0. This turns off Q0511 and the radio turns off. Notice that EMER TRIG also goes to U0104-D5. This
is where the appropriate microprocessor is alerted to the emergency condition. If the radio was
already on when emergency was triggered then B+ CTRL would already be high and EMER TRIG
going high due to the emergency condition would have no effect on Q0510, i.e. switching on Q0511
when it is already on.

Mechanical On/Off

(Refer to schematic Page 10-30 for reference)
This refers to the typical on/off switch, located on the control head, and which turns the radio on and
off.
U0502 is fed by A+, and is therefore always on and providing 8 V on MIC VOLTAGE. When the
Mechanical on/off switch is pressed, the MIC IN line is momentarily grounded setting the ON/OFF
input of U0510-6 low.
Similar to the emergency operation described previously, when U0510-6 ON/OFF is above 1/3 of the
supply voltage at U0510-14, it will cause the device to internally ground U0510-1, which in turn holds
capacitor C0511 in a discharged state. The device also keeps U0510-5 SW B+ SENSE at a low
voltage. When ON/OFF goes below 1/3 of the device supply voltage, U0510 disables the discharge
mechanism at pin 1 allowing the capacitor C0511 to charge through R0512. The charging rate is set
by the values of R0512 and C0511. When the voltage at pin 2 goes above 2/3 supply voltage, the
device sets pin 5 SW B+ SENSE high which in turn switches on Q0510 enabling the radio to turn on
to begin operation. U0510 will keep pin 5 high for a period set by R0512 and C0511 which for 200K/
1 uF equals 220 ms.
68P81083C20-D
7-3
December 6, 2004