Figure 7-3. Transmit Signalling Paths - Motorola MCS 2000 Service Instructions Manual

7-20
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 uP first programs the ASFIC (U0200) to the proper filter and gain
settings. It then begins strobing U0200-G1 (TX DATA) with a pulse when the data is supposed to
change states.
MICRO
CONTROLLER
U0200's 5-3-2 State Encoder (which is in a 2-state mode) is then fed to the post-limiter summer block
and then the splatter filter. From that point it is routed through the modulation attenuators and then
out of the ASFIC to the RF board. MPT 1327 and MDC are generated in much the same way as
Trunking ISW. However, in some cases these signals may also pass through a data pre-emphasis
block in the ASFIC. Also these signalling schemes are based on sending a combination of 1200 Hz
and 1800 Hz tones only. Microphone audio is muted during High Speed Data signalling.
Dual Tone Multiple Frequency (DTMF) Data
DTMF data is a dual tone waveform used during phone interconnect operation. It is the same type of
tones which are heard when using a "Touch Tone" telephone.
There are seven frequencies, with four in the low group (697, 770, 852, 941 Hz) and three in the high
group (1209, 1336, 1477 Hz).
The high-group tone is generated by the µP (U0103-74) strobing U0200-G1 at six times the tone
frequency for tones less than 1440 Hz or twice the frequency for tones greater than 1440 Hz. The
low group tone is generated by the µP (U0103-73) strobing U0200-G2 (DTMF CLOCK) at six times
the tone frequency. Inside U0200 the low-group and high-group tones are summed (with the
amplitude of the high group tone being approximately 2 dB greater than that of the low group tone)
and then pre-emphasized before being routed to the summer and splatter filter. The DTMF waveform
then follows the same path as was described for high-speed data.
December 6, 2004
Controller Section Theory of Operation: Audio and Signalling Circuits
HS
SUMMER
5-3-2 STATE
G1 HIGH SPEED
ENCODER
CLOCK IN
G2 DTMF DTMF
ENCODER
CLOCK
ASFIC
U0200
C3 LOW SPEED PL
CLOCK ENCODER

Figure 7-3. Transmit Signalling Paths

SPLATTER
FILTER
LS
SUMMER
H8
AUDIO MOD
ATTENUATOR
TO RF
SECTION
(VCO)
68P81083C20-D