Motorola Cdm And Pro Series Detailed 68p81091c63 O Manual

Theory of Operation2-7
2.2.10 Normal Microprocessor Operation
The µP is configured to operate in one of two modes: expanded or bootstrap. In expanded mode, the 
µP uses external memory devices to operate. In bootstrap mode, the µP uses only its internal 
memory. 
During normal operation of the radio, the µP is operating in expanded mode and the µP (U0101) has 
access to three external memory devices: U0121 (EEPROM), U0122 (SRAM), and U0111 
(EEPROM). Also, within the µP there are three KBs of internal...

2-8Theory of Operation
U0101-69 is the high reference voltage for the A/D por ts on the µP. Capacitor C0101 filters the +5 
volt reference. If this voltage is lower than +5 volt, the A/D reading is incorrect. Likewise U0101, pin 
68 is the low reference for the A/D ports. This line is normally tied to ground. If this line is not 
connected to ground, the A/D readings could be incorrect.
2.2.11 Static Random Access Memory (SRAM)
The SRAM (U0121) contains temporary radio calculations or parameters that can...

Theory of Operation2-9
2.3.2 Transmit Audio Circuits
Refer to Figure 2-3 for the descriptions that follow.
Figure 2-3.   Transmit Audio Paths
2.3.3 Microphone Input Path
The radio supports two microphone input paths. One from the control head external microphone 
accessory connector J0501, pin 2, and one from the microphone auxiliary path (FLAT TX AUDIO) via 
accessory connector J0501, pin 5. The microphones require a DC biasing voltage provided by a 
resistive network.
The two microphone audio input...

2-10Theory of Operation
Multi switch U0251 controlled by ASFIC CMP por t GCB4 selects either the external microphone 
input signal or the voice storage playback signal for entering the ASFIC CMP at pin 48. The audio 
signal at U0221-48 (TP0222) is approximately 14mVrms for 1.5kHz or 3kHz of deviation with 
12.5kHz or 25kHz channel spacing.
The FLAT TX AUDIO signal from accessory connector J0501-5 is fed to the ASFIC CMP (U0221, pin 
42) through C0541 and line FLAT TX RTN.
The ASFIC has an internal AGC...

Theory of Operation2-11
2.3.4 Transmit Signalling Circuits
Refer to Figure 2-4 for the descriptions that follow.
Figure 2-4.   Transmit Signalling Paths
The three types of transmit signalling paths are as follows:
• Sub-audible data (PL/DPL/connect tone) summed with transmit voice or signalling
• DTMF data for telephone communication between trunked and conventional systems
• Audible signalling 
2.3.4.1  Sub-Audible Data (PL/DPL)
Sub-audible data implies signalling whose frequency/data rate is below...

2-12Theory of Operation
2.3.4.2  High Speed Data
High speed data refers to the 3600 baud data waveforms, known as inbound signalling words (ISWs) 
used in a trunking system for high speed communication between the central controller and the 
radio. To generate an ISW, the µP first programs the ASFIC CMP (U0221) to the proper filter and 
gain settings. It then begins strobing U0221-19 (HSIO) with a pulse when the data is supposed to 
change states. U0221’s 5-3-2 state encoder, which is in a 2-state mode,...

Theory of Operation2-13
2.3.5 Receive Audio Circuits
Refer to Figure 2-5 for the descriptions that follow.
Figure 2-5.   Receive Audio Paths
2.3.5.1  Squelch Detect
The squelch detect circuits are all contained within the ASFIC CMP as shown in Figure 2-5. The 
radio’s RF circuits are constantly producing an output (DISC AUDIO) at the discriminator IF IC. The 
output signal is applied to the ASFIC CMP’s squelch detect circuits DISC input (U0221, pin 2). The 
squelch signal entering the ASFIC CMP is...

2-14Theory of Operation
2.3.5.2  Audio Processing and Digital Volume Control
The receiver audio signal (DISC AUDIO) enters the controller section from the IF IC where it is AC 
coupled by C0227 before entering the ASFIC CMP via the DISC input at U0221, pin 2. The signal is 
then applied to both the audio and the PL/DPL paths.
The signal on the audio path is applied to a programmable amplifier, whose setting is based on the 
channel bandwidth being received, an LPF filter to remove any frequency...

Theory of Operation2-15
2.3.5.4  Handset Audio
Certain accessories have a self contained speaker which requires a different voltage level than that 
provided by U0271. For those devices, HANDSET AUDIO is available at control head connector 
J0401, pin 7.
The received audio from the output of the ASFIC CMP’s digital volume attenuator and buffered by 
U0211, pin 1, is also routed to U0211, pin 9 where it is amplified by 20 dB. This is set by the 10k/
100k combination of R0261 and R0262. This signal is...

2-16Theory of Operation
2.3.6 Receive Signalling Circuits
Refer to Figure 2-6 for the descriptions that follow.
Figure 2-6.   Receive Signalling Paths
2.3.6.1  Sub-Audible Data (PL/DPL) and High Speed Data Decoder
The ASFIC CMP (U0221) filters and limits all received data. The data enters the ASFIC CMP at input 
DISC (U0221, pin 2). Inside U0221 the data is filtered according to data type (HS or LS), then it is 
limited to a 0-5V digital level. The MDC and trunking high speed data appear at U0221, pin...