Motorola pro7100 Manuel de service Page 30

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2-16 Theory 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 19, where
it connects to the µP U0101, pin 82
The low speed limited data output (PL, DPL, and trunking LS) appears at U0221, pin 18, where it
connects to the µP U0101, pin 80.
The low speed data is read by the µP at twice the frequency of the sampling waveform; a latch
configuration in the ASFIC CMP stores one bit every clock cycle. The external capacitors C0236, and
C0244 set the low frequency pole for a zero crossings detector in the limiters for PL and HS data.
The hysteresis of these limiters is programmed based on the type of received data.
2.3.6.2 Alert Tone Circuits
When the software determines that it needs to give the operator an audible feedback for a good key
press, or for a bad key press, or radio status (trunked system busy, phone call, circuit failures), it
sends an alert tone to the speaker. It does so by sending SPI BUS data to U0221 which sets up the
audio path to the speaker for alert tones. The alert tone itself can be generated in one of two ways:
internally by the ASFIC CMP, or externally using the µP and the ASFIC CMP.
The allowable internal alert tones are 304, 608, 911, and 1823Hz. In this case a code contained
within the SPI BUS load to the ASFIC CMP sets up the path and determines the tone frequency, and
at what volume level to generate the tone. (It does not have to be related to the voice volume setting).
For external alert tones, the µP can generate any tone within the 100-3000Hz audio band. This is
accomplished by the µP generating a square wave which enters the ASFIC CMP at U0221-19. Inside
the ASFIC CMP this signal is routed to the alert tone generator
The output of the generator is summed into the audio chain just after the RX audio de-emphasis
block. Inside U0221 the tone is amplified and filtered, then passed through the 8-bit digital volume
attenuator, which is typically loaded with a special value for alert tone audio. The tone exits at U0221-
41 and is routed to the audio PA like receive audio.
DET AUDIO
DISCRIMINATOR AUDIO
FROM RF SECTION
(IF IC)
19
18
25
2
82
80
DISC
PLCAP2
LSIO
HSIO
DATA FILTER
AND DEEMPHASIS
LIMITER
FILTER
LIMITER
ASFIC_CMP
U0221
MICRO
CONTROLLER
U0101
85
44
8
PLEAP
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