Latches And Relay Drivers Circuit - Motorola F2265A Owner's Manual

Theory of Operation
•
Shorts the sensor outputs to the ground after the
tuning process is completed.
•
Stores the tuning data for each frequency used.
•
Keeps the tuning data storage alive after the ATU is
turned off for a minimum of 0.5 second (this
function is necessary for the 50ms of DC
interrupting when the channel is changed).
•
Enters idle state after the tuning process is
completed and the tuning data is stored. This
feature minimizes the noise on the receive path
during reception.
3.3.3.1 Frequency Counter
The frequency sample FREQ from the RF Sensor is
converted to square wave by U3 and divided by 128 by
U15 and U16. The divided signal is applied to the
microprocessor input PA7. The microprocessor counts
the signal frequency in a 20 millisecond time slot.
Therefore the frequency measurement accuracy is 6400
Hz calculated as follows:
1
−
3
⋅
20 10 sec
3.3.3.2 Sensor Data Processing
The sensor data is applied to microprocessor inputs PE0
through PE7. An internal A/D converter converts the
data into a digital format, in which all the calculations
are performed. The following calculations and
decisions are done:
•
Calculating the VSWR:
VSWR
•
Calculating the location on the Smith Chart in
relation to the G=1 circle:
- if V >V then G<1;
,
g f
- if V <V , then G>1.
g f
•
Verifying that the tune power at the ATU input is
within the predefined range (3-6 W):
- if V <V or V
low
f
rejected and the ATU is bypassed.
3-6
× =
128 6400 Hz
V
+
1 R
V
=
F
V
−
R
1
V
F
>V , the tuning request is
high
f
•
Determining the load characteristics:
- if PH-C>PH-L, the load is capacitive;
- if PH-L>PH-C, the load is inductive.
3.3.3.3 Shorting the Sensor Outputs
After the tuning process is completed, the Tuner Logic
circuit shorts the signal lines from the sensors to a
ground, to protect the logic circuits and the sensor
components from high
transmission.
A 100 Ω resistor and a FET switch are connected
between the sensor outputs and the ground (R45-R49
and Q27-Q31). A
microprocessor output PA6 turns on the FET switches.
The signal F_SWITCH
microprocessor at pin PA5 controls the shorting of the
frequency sampling circuit in the RF Sensor. Refer to
paragraph 3.3.1.4 for a detailed description of the
frequency sampling circuit.
3.3.3.4 Tune Data Memory
The Tuner Logic circuit saves the tuning data for each
tuned frequency in RAM U9. This data is stored as long
as the ATU is on.
3.3.3.5 Relay Driver Activation
The microprocessor controls the relay activation via the
SPI BUS serial bus. The serial control data is passed to
the Latch and Relay Drivers circuit.
3.3.4 LATCHES AND RELAY DRIVERS
CIRCUIT
The relay control data received from the Tuner Control
circuit via the SPI BUS, is applied to shift registers
U10-U13. The shift registers convert the serial data into
parallel. Each shift register provides 8 bits, all of which
are combined into
(DRIVERS_BUS).
The DRIVERS_BUS bits are applied to 26 transistors
that actually drive the relays via the RELAY_BUS.
power during normal
control signal from
generated by
a 32 bit parallel
the
the
bus