Shure UC2, Руководство по обслуживанию

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Shure UC2 Hand-Held UHF Transmitter
6 Characteristics 25A1044 (RI)
Memory Section
The memory section consists of U302, a non-volatile, Electrically
Erasable/Programmable Read Only Memory (
EEPROM
) that stores the
mapping of the compatible groups and channels. The microcontroller
serially communicates with this part via data and clock lines to read the
frequency corresponding to the Group and Channel position.
The ability to write to the memory occurs during factory programming
only. During normal usage, this memory is used as a look-up table only.
R335 and R305 resistors allow the clock and data lines to be driven
independently of the microcontroller port pin states during in-circuit pro-
gramming of the
EEPROM
.
Battery Management Section
The U303 microcontroller provides low battery shutdown. The shut-
down threshold is 1.88 Vdc
±
10%. A voltage lower than the shutdown
threshold on U303, pin 17, shuts down the transmitter. Resistors R308
and R309 divide down the battery voltage for U303; a battery voltage
less than 5.65 Vdc must shut down the transmitter.
This auto shutdown disables the audio tone key mix, mutes the rf
output, and powers down the rf output amplifier section. The current
draw from a 9 Vdc battery in this state is 14
±
2.0 mA, and the battery
fuel gauge is not functional. Turning off the power switch completely
shuts off the transmitter.
The audio circuit description section provides information for the
battery fuel gauge circuit description.
Rotary Switches for Frequency Selection
A 10-position Group switch (S302) and a 16-position Channel switch
(S301) select the transmitter frequency. Both rotary switches share the
same U303 microcontroller port pins (3 through 6) for a multiplexed
switch read operation. The individual switches are selected by U303,
pins 7 and 8. Resistors R4, R300, R302, and R303 are the pull-ups for
the switch position read. Diode packs D301 through D304 isolate the
switches during the multiplexed read operation.
The multiplexed scheme to read switches does not allow incorporat-
ing switch change detection based on interrupts. Also, the switches can-
not be constantly scanned to determine changes because the scanning
frequency being in audio range is difficult to filter out.
In a steady state, the switch selector common pins are inputs to the
U303, pins 7 and 8, while U303, pins 3 through 6, are outputs. In this
state, pins 4, 5, and 6 are held low while pin 3 is held high. This forces
logic high level on switch selector pins if the switches are set on odd
positions. For even position settings, the contact on pin 1 is open from
the switch common pin and the internal pull-down resistors force logic
low to U303, pins 7 and 8.