Motorola CP150TM - Manual (Page 26)

June, 2005 6880309N62-C
3-6 Controller Theory of Operation: Controller
3.1.2.4 PTT Circuits
The internal side-mounted PTT switch (S441) is sensed directly by microprocessor port PJ0 (U401
pin 71). External mic PTT is sensed by measuring the current drawn through the accessory
connector (J471-4) by the mic cartridge (which is in series with the accessory PTT switch). This
current is drawn through the base (pin 5) and emitter (pin 4) of a transistor in Q470, causing its
collector (pin 3) to supply a logic-high to microprocessor port PJ1 (pin 72).
3.1.2.5 VOX Operation
VOX audio accessories do not have a PTT switch. Instead, the mic cartridge is wired directly from
J471-4 to ground. If the radio has been programmed for VOX operation and the VOX accessory is
plugged in prior to turning the radio on, the current drawn by the cartridge will turn on Q470 (pins 3-
4-5) and a logic high will be seen at port PJ1 at turn-on. The microprocessor then assumes VOX
operation, with PTT controlled by the presence of audio at the mic cartridge. A dc voltage
proportional to the audio level at the input of the ASFIC_CMP (U451 pin 46) is fed to an A/D input of
microprocessor U401 (pin 62). During VOX operation, PTT is activated when the dc level exceeds a
preset threshold.
3.1.2.6 Battery Charging Through Microphone Jack
A wall-type charging power supply may be connected to the 2.5 mm microphone jack (part of
accessory connector J451). The voltage present at the tip contact (pin 4) is applied to the center
charging contact of the battery via diode D470. Another diode, internal to the battery, applies this
voltage to the (+) battery terminal. Only the recommended charger and battery type should be
charged in this manner.
Different battery types contain internal resistors connected from the BATT_CHARGE contact to
ground, which is routed to the microprocessor as BATT_DETECT. A voltage divider is formed with
R255 producing a DC voltage which is read by microprocessor port PE2 (pin 65). This allows the
software to recognize the battery chemistry being used and adjust the battery gauge for best
accuracy. The value of R255 is chosen so that the voltage at the BATT_CHARGE node (cathode of
D470) is never low enough to turn on the EXT_MIC_PTT sense transistor (part of Q470).
3.1.2.7 Programming and Flashing Through Microphone Jack
The ring contact on the 2.5 mm microphone jack is used for reading, programming or re-flashing the
radio using CPS. This contact (J471 pin 6) is routed to ports PD0_RXD (data into uP, pin 97) and
PD1_TXD (data out of uP, pin 98). Transistor Q410 isolates the input and output functions by
allowing PD1 to pull the line low, but does not affect incoming data from being read by port PD0.
To re-flash the radio (overwrite the software in the Flash ROM with new software), the radio must
power up in the boot mode. This is accomplished by using a flash adapter accessory, which provides
SCI communication with the programming ring contact (J471 pin 6) and also allows a negative
voltage (negative 9 volts dc via a 1K resistor) to be applied to the tip contact (J471 pin 4). This
voltage is sufficient to turn on the base-emitter junction (pins 1 and 2) of Q472 via L471, D471,
VR472 and R471. Pin 6 of Q472 goes high, turning on Q471 (pins 3 and 4) and pulling the
BOOT_ENA line (ports MODA and MODB of the microprocessor) low. Cycling power generates a
reset which causes the radio to boot in the flash mode.