Receive Signalling Circuits; Sub-Audible Data (Pl/Dpl) And High Speed Data Decoder; Alert Tone Circuits - Motorola GTX/LCS 2000 Service Manual

Receive Signalling Circuits

DET AUDIO
DISCRIMINATOR AUDIO
FROM RF SECTION
(IFIC)
Sub-audible Data (PL/DPL)
and High Speed Data Decoder

Alert Tone Circuits

Refer to the following sections.
G1
HIGH SPEED
CLOCK
DATA FILTER
LIMITER
& DEEMPHASIS
J7
PL
ASFIC U0201
IN
FILTER LIMITER
LOW SPEED
LIM CAP
C5
Figure 7-6 Receive Signalling Path.
The ASFIC (U0201) is used to filter and limit all received data. The data enters
the ASFIC at U0201-J7. Inside U0201 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 U0201-G4, where it connects to the µP U0101-11.
The low speed limited data output (PL, DPL, and trunking LS) appears at U0201-
A4, where it connects to the µP U0101-10. While receiving low speed data, the
µP may output a sampling waveform depending on the sampling technique to
U0201-C3 between 1 and 2 kHz.
The low speed data is read by the µP at twice the frequency of the sampling
waveform; a latch configuration in the ASFIC stores one bit every clock cycle.
The external capacitors C0226, C0225, and C0223 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.
Note:
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 U0201 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, or externally using the µP and the ASFIC.
C3
LOW SPEED
CLOCK
G4
RX
LIM
OUT
A4
PL
LIM
RX LIM
CAP
J3
During HS data, the µP may generate a sampling waveform
seen at U0201-G1.
6 5
11
MICRO
CONTROLLER
U0101
10
Theory of Operation 7-21