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Page 16 RF Technology T70/T150

5.11 Microprocessor Controller 5 CIRCUIT DESCRIPTION

A DMTX board can also cause the exciter to key up. When a TX (or TTL_TX) signal

is received by the DMTX board, it pulls pin 6 of JP15 low, which, in turn asserts the

PTT_WIRE_OR signal, causing the microprocessor (U13) to key the exciter up.

5.11 Microprocessor Controller

The microprocessor controller circuit uses a single-chip eight bit processor and several

support chips. The processor U13 includes non-volatile EE memory for channel

frequencies, tones, and other information. It also has an asynchronous serial port, a

synchronous serial port and an eight bit analog to digital converter.

The program is stored in U5, a CMOS EPROM. U4 is an address latch for the low

order address bits. U2 is used to read the channel select lines onto the data bus. U11

is an address decoder for U5 and U2. U3 is a supervisory chip which keeps

the processor reset unless the +5 Volt supply is within operating limits. U1 translates

the asynchronous serial port data to standard RS232 levels.

The analog to digital converter is used to measure the forward and reverse power,

tuning voltage and dc supply voltage.

If the processor detects that the PTT_WIRE_OR signal is asserted low, it will attempt

to key the exciter up. It will attempt to key the VCO through Q10, and if the LD pin

goes high, it will switch the 9.2 Volt transmit line through Q14 and Q16. Asserting

Q16 has the effect of also asserting the yellow Tx LED (D12) on the front panel,

enabling the local 25W power amplifier, and causing the T/R Relay output to be

pulled low. D24 is 30 volt zener which protects Q25 from both excessive voltages or

reverse voltages.

Should there be a problem with either the tuning volts, or the battery voltage, the VCO

locking, the forward power, or the reverse power, the microprocessor will assert the

ALARM LED through Q1. Depending on the setting of Jumper JP19, the ALARM

signal can be brought out on pin 7 of P3.

5.12 Voltage Regulator

The dc input voltage is regulated down to 9.4 Vdc by a discrete regulator circuit. The

series pass transistor Q23 is driven by error amplifiers Q8 and Q18. Q9 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 proof by virtue of the component current and

power ratings. The maximum current and dissipation rating of the pass transistor can

not be exceeded under any load condition.

The discrete component circuit provides much better line isolation and lower dropout

voltage than can be obtained with current integrated circuit regulators.

The +5 Volt supply for the logic circuits is provided by an integrated circuit regulator

U14 which is run from the regulated 9.4 Volt supply.

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RF Technology R150 Betriebsanleitung Seite 16