High Speed Data; Dual Tone Multiple Frequency (Dtmf) Data - Motorola CM200 Service Manual

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8.2

High Speed Data

High speed data refers to the 3600 baud data waveforms, known as Inbound Signaling 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 (U504) to the proper filter and
gain settings. It then begins strobing U504-pin 19 (HSIO) with a pulse when the data is supposed to
change states. U504'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
attenuator and then out of the ASFIC CMP to the RF board. MDC is 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 CMP. Also these signaling schemes are based on sending a
combination of 1200 Hz and 1800 Hz tones only. Microphone audio is muted during high speed data
signaling.
8.3

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, 941 Hz) and three in the
high group (1209, 1336, 1477 Hz). The high-group tone is generated by the µP (U403-46) strobing
U504-19 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 ASFIC CMP, controlled by the
µP via SPI bus. Inside U504 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