Operating instructions

RF Technology R350/R500 Page 13
5.8 Microprocessor Controller 5 CIRCUIT DESCRIPTION
5.8 Microprocessor Controller
The microprocessor controller circuit uses an advanced eight bit processor and several
support chips. The processor U15 includes EE memory for channel frequencies, tones,
and other information. It also acts as an asynchronous serial port, a synchronous serial
port and an analogue to digital converter.
The program is stored in U12, a CMOS EPROM. U13 is an address latch for the low
order address bits. U11 is used to read the channel select lines onto the data bus. U7 is
an address decoder for U11 and U12. U14 is a supervisory chip which keeps the
processor reset unless the +5 Volt supply is within operating limits. U16 translates the
asynchronous serial port data to standard RS232 levels.
The analog to digital converter is used to measure the received signal strength, tuning
voltage, dc supply voltage and the carrier squelch setting.
5.9 Carrier Operated Switch
The carrier operated switch is an opto-coupled (ISO1) output. Internal jumpers (JP4,
JP7, JP8, JP9) can be connected to provide loop source, loop switch, free switch and
various other configurations.
The COS can be set to be active (switch closed) on carrier or active in the absence of
carrier.
The generic term ``Carrier Operated Switch'' may be misleading in this case. SINCE,
if a sub-audible tone has been programmed for the channel in use, the COS is
controlled by carrier and tone detection.
5.10 Voltage Regulator
The dc input voltage is regulated down to 9.4 Vdc by a discrete regulator circuit. The
series pass transistor Q20 is driven by error amplifiers Q21 and Q22. Q23 is used to
start up the regulator and once the circuit turns on, it plays no further part in the
operation.
This circuit is short circuit and overload protected. It provides much better line
isolation and lower dropout voltage than can be obtained with current integrated
circuit regulators.
6 Alignment Procedure
The following procedures may be used to align the receiver for optimum performance.
Normally only RF alignment will be required when changing frequencies. IF
alignment should only be necessary after repairs on that part of the circuit.