Motorola Pr400 Detailed 6881096c25 B Manual

Chapter 2 DC Power Distribution
2.1 DC Regulation and Distribution
A block diagram of the DC power distribution throughout the radio is shown in Figure 2-1.
Figure 2-1.  DC Power Distribution Block Diagram
Battery voltage enters at connector J301 and is routed through fuse F301 to become USWB+. 
VR301 protects against ESD, and D301 provides reverse polarity protection. This voltage is routed 
to:
• FET switch Q170 in the TX power control circuit (turned on during transmit)
• TX power amplifier module...

June, 20056881096C25-B
2-2DC Power Distribution: DC Regulation and Distribution
When the radio is turned on, SWB+ is present and is applied to:
• transistor switch Q494 (pins 1 and 6) which turns on Q493
• RX audio power amplifier U490
• voltage divider R420/R421 and port PE0, a microprocessor A/D input which measures battery 
voltage and radio on/off status
The output of FET switch Q493 is applied to the control pins of regulators U310, U320 and U330, 
turning them on. The following regulators are...

Chapter 3 Controller Theory of Operation
3.1 Controller
The controller provides the following functions:
• interface with controls and indicators
• serial bus control of major radio circuit blocks
• encoding and/or decoding of selective signaling formats such as PL, DPL, MDC1200 and Quik-
Call II
• interface to CPS programming via the microphone connector
• storage of customer-specific information such as channel frequencies, scan lists, and signaling 
codes
• storage of factory tuning parameters such as...

June, 20056881096C25-B
3-2Controller Theory of Operation: Controller
3.1.1.1  Memory Usage
Radio operation is controlled by software that is stored in external Flash ROM memory (U404).  
Radio parameters and customer specific information is stored in external EEPROM (U402). The 
operating status of the radio is maintained in RAM located within the microprocessor. When the radio 
is turned off, the operating status of the radio is written to EEPROM before operating voltage is 
removed from the...

6881096C25-BJune, 2005
Controller Theory of Operation: Controller3-3
In order for each circuit block to respond only to the data intended for it, each peripheral has its own 
chip select (or chip enable) line. The device will only respond to data when its enable line is pulled 
low by one of the microprocessor ports, as follows:
• port PD5 (U401 pin 2) for the audio filter IC
• port PH0 (U401 pin 47) for the synthesizer IC
• port PH4 (U401 pin 43) for the option board/display enable
• port PD6 (U401 pin...

June, 20056881096C25-B
3-4Controller Theory of Operation: Controller
The microprocessor reset line (pin 94) can be controlled directly by the digital 3.3 V regulator (U320 
pin 7), the microphone jack (part of accessory connector J471) via Q472 and Q471, and the 
microprocessor itself. U320 pulls the reset line low if the digital 3.3 V source loses regulation. This 
prevents possible MOS latch-up or overwriting of registers in the microprocessor because the reset 
line is higher in voltage than the...

6881096C25-BJune, 2005
Controller Theory of Operation: Controller3-5
• 2.5 volt dc reference source
• Microprocessor clock generation (from the 16.8 MHz reference oscillator input)
The parameters of U451 that are programmable are selected by the microprocessor via the CLOCK 
(U451 pin 21), DATA (U451 pin 22) and chip enable (U451 pin 20) lines.
RX audio buffer U510 amplifies the audio level from the DEMOD output of the IFIC before being 
applied to the audio filter IC input (DISC, U451 pin 2). The buffer...

June, 20056881096C25-B
3-6Controller Theory of Operation: Controller
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...

Chapter 4 136-162 MHz VHF Theory Of Operation
4.1 Introduction
This chapter provides a detailed theory of operation for the radio components. Schematic diagrams 
for the circuits described in the following paragraphs are located in Chapter 7 of this manual.
4.2 VHF Receiver
The VHF receiver covers the range of 136-162 MHz and provides switchable IF bandwidth for use 
with 12.5 kHz or 20/25 kHz channel spacing systems. The receiver is divided into two major blocks as 
shown in Figure 4-1.
•Front End
•...

June, 20056881096C25-B
4-2136-162 MHz VHF Theory Of Operation: VHF Receiver
constant at 6.2 mA regardless of device and temperature variations, for optimum dynamic range and 
noise figure.
The output of the RF amplifier is applied to the interstage filter, a fixed-tuned 3-pole series-coupled 
resonator design having a 3 dB bandwidth of 54 MHz and insertion loss of 1.8 dB. This filter has an 
image rejection of 40 dB at 226 MHz, with increasing attenuation at higher frequencies.
The output of the...