MC68HC05F8 Datasheet, PDF (82/126 Pages) Motorola, Inc – High-density complementary metal oxide semiconductor(HCMOS) microcontroller unit

Freescale Semiconductor, Inc.
3.58MHz ÷ 2
Row Frequency
Divider
PLA Sinewave PLA ⁶
Scanner 28 x 6-bits
Sine / Square
Wave Select
MSB
MUX
LSB
5
5
Row Frequency Control Register
Column Frequency Control Register
Tone Control
Tone Control
register bits 4 & 5 register bits 6 & 7
Data
TGER
MS1
Validator
TGEC
MS0
5
6-bit Resistor
Ladder
TONEX
+ ^TONEOUT
+
current summer
+
active low-pass filter
Column Frequency
Divider
PLA Sinewave PLA ⁶ Sine/Square ⁶ 6-bit Resistor High Group
Scanner 28 x 6-bits
Wave Select
Ladder Pre-emphasis
Figure 9-1 DTMF/Melody Generator Block Diagram
sampling rate of the desired “staircase sine wave”. This pulse train then clocks a divide-by-28
binary counter (PLA scanner) whose 28 decoded outputs sequentially scan 28 memory locations
9
of a 28x6 sine wave generator (PLA) in 28 time steps (M). The 6 resulting digital sine wave bits
are then fed separately to a 6-bit resistor ladder to produce a current signal.
The method for generating a square wave tone in a path is similar to that of a sine wave tone
except that only the most significant bit of a sine wave PLA is fed to the 6-bit resistor ladder (the
other 5 bits are masked by the Sine/Square wave select) to produce a current signal. The resulting
square wave tone has exactly the same frequency and phase as a sine wave tone for the same
frequency control register value.
After obtaining the current signals from the row and column paths, the row current signal is first
attenuated by 2dB, and is then summed with the column current signal, and is finally fed to an
active 7KHz low pass filter to reduce harmonic distortion. The resulting DTMF or melody signal is
output to the TONEOUT pin, which is normally buffered to drive a buzzer.
The generator provides not only DTMF and melody but also a square wave pacifier tone (Tone).
This signal is also extracted from the most significant bit of the sine wave PLA of the row path, but
is not subjected to the filter. The ToneX signal is output to the TONEX pin, which is normally
connected to a loudspeaker.
MOTOROLA
9-2
DTMF/MELODY GENERATOR
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TPG
MC68HC05F8