File Number 1257.4
Monolithic Silicon COS/MOS Dual-Tone
Multifrequency Tone Generator
The CD22859 is a CMOS dual-tone multifrequency (DTMF)
tone generator for use in dual-tone telephone dialing
systems. The device can easily be interfaced to a standard
push-button telephone keyboard to provide enabling
operation directly with the telephone lines.
The CD22859 generates standard DTMF sinusoidal dialing
tones from an on-chip reference crystal oscillator. The
reference oscillator uses an inexpensive 3.579545MHz color
TV crystal to create highly stable and accurate tones. The
sinusoidal tones are digitally synthesized by a stair-step
One of four low-frequency band row tones and one of four
high-frequency band column tones are selected by driving
one of the four row inputs and one of the four column inputs
low. Simultaneous selection of more than one row input
and/or more than one column input will inhibit tone
generation, or generate a single-tone sinusoid. These
operating modes are described in the functional truth table.
Control logic is included to allow easy interface to standard
K500-type telephones. Two CMOS outputs (TX, RX) capable
of driving external pnp receiver and transmitter muting
transistors are provided. A low input to the CD pin inhibits
tone generation, turns off the reference oscillator and causes
TX and RX outputs to go to logic ‘0’. During tone generation
mode, CD = 1 and TX, RX = logic 1.
The row, column and CD inputs are provided with pull-up
resistors to allow the use of SPST switch matrixes.
PART NUMBER RANGE (oC)
-40 to 85 16 Ld PDIP
• Mute Drivers On-Chip
• Device Power can Either be Regulated DC or Telephone
• Use of an Inexpensive 3.579545MHz TV Crystal Provides
High Accuracy and Stability for all Frequencies
• For Use In Dual-tone Telephone Dialing Systems
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-800-4-HARRIS or 407-727-9207 | Copyright © Harris Corporation 1999