DTMF signal sending / receiving circuit chip MT8880
One, Features:
(1) DTMF8880 is a CMOS large-scale integrated circuit with low power consumption (52mW), and the sending and receiving circuits are integrated in one chip, so the degree of integration is high.
(2) Programmable control, easy to interface with microcomputer, microcomputer can control the receiving part of the working principle is the same as DTMF signal receiver MT8870. The transmission part adopts the switched capacitor D / A converter, so the DTMF signal distortion is small, the frequency accuracy is high, and the on-chip counter accurately times the duty time of the dual audio mode.
(3) RSO is the input terminal for register selection; Φ 2 is the clock input terminal, cooperates with R / W to complete reading and writing data; IRQ / CP is the interrupt request signal output terminal, OC output circuit, or in CP mode, it outputs a square wave, marking Receive DTMF signaling codec and various formula mode selection.
(4) With a variety of working modes, so the function is very strong.
two, Pin arrangement
MT8880 schematic
three, Internal register
Internal register function
RSO | R / W | Features |
0 | 0 | Write transmit data register |
0 | 1 | Read receive data register |
1 | 0 | Write control register |
1 | 1 | Read status register |
Control Register ( CRA) function
Control bit | Name and function | Explanation |
b0 | Tout tone output | Logic " 1" enables tone output |
b1 | CP / DTMF mode. control | Logic " 1" is CP mode. When b2 = 1, for example, input the busy tone of the phone, and output a busy tone square wave |
b2 | IRQ interrupt enable | Logic " 1" enables interrupt mode. When b1 = 0, the DTMF signal is received or a new two-tone signal is ready to be sent, and the DTMF / CP pin level changes from high to low. |
b3 | RSEL register selection | Logic " 1" allows selection of CRB |
Control register ( CRB) function
Control bit | Name and function | Say Bright |
b 0 | BURST dual tone group mode | Logic " 0" enables dual tone group mode |
b1 | TEST experiment mode | Logic " 1" enables experimental mode. In this mode, the IRQ / CP pin outputs a delay control signal (CRA b1 = 0) |
b2 | S / D single and double tone generation | Logic " 0" allows to generate DTMF, otherwise, output single tone |
b3 | C / R column / line sound selection | b2 = 1, " logic" enable to generate single tone signal |
Status register function
Status bit | name | Status flag set | Status flag clear |
b0 | IRQ | An interruption occurred; b1 or b2 = 0 | Read status register clear |
b1 | Transmit register empty (group mode) | End of pause: ready to send new data | Same as above |
b2 | Receive register full | Receive register data is valid | Same as above |
b3 | DELAYED-STEERING | Set when no DTMF signal is detected | Cleared when DTMF signal is detected |
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