High Speed Data; Dual Tone Multiple Frequency (Dtmf) Data - Motorola GM-950 Manual

5.2

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 (U0201) to the proper filter and gain
settings. It then begins strobing U0201-G1 (TRK CLK IN) with a pulse when the data is supposed to
change states. U0201'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.
5.3

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, 941Hz) and three in the high
group (1209, 1336, 1477Hz).
The high-group tone is generated by the µP (U0101-5) strobing U0201-G1 at six times the tone
frequency for tones less than 1440Hz or twice the frequency for tones greater than 1440Hz. The low
group tone is generated by the µP (U0101-7) strobing U0201-G2 (DTMF CLCK) at six times the tone
frequency. Inside U0201 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.
Theory of Operation
Transmit Signalling Circuits
5C.3-13