MT8885
Pin Description
Pin #
Name
24
15
28
18
IRQ/CP
Description
Data Sheet
Interrupt Request/Call Progress
(open drain) output. In interrupt mode, this output
goes low when a valid DTMF tone burst has been transmitted or received. In call
progress mode, this pin will output a rectangular signal representative of the input
signal applied at the input op-amp. The input signal must be within the bandwidth
limits of the call progress filter, see Figure 8.
Power-Down
(input). Active High. Powers down the device and inhibits the oscillator.
IRQ and TONE output are high impedance. Data bus is held in tri-state. This pin has
no internal pulldown resistor. Therefore, must be tied to logic low when not used.
Microprocessor data bus. High impedance when CS = 1 or DS =0 (Motorola) or RD =
1 (Intel). TTL compatible.
Early Steering
output. Presents a logic high once the digital algorithm has detected
a valid tone pair (signal condition). Any momentary loss of signal condition will cause
ESt to return to a logic low.
Steering Input/Guard Time
output (bidirectional). A voltage greater than V
TSt
detected at St causes the device to register the detected tone pair and update the
output latch. A voltage less than V
TSt
frees the device to accept a new tone pair. The
GT output acts to reset the external steering time-constant; its state is a function of
ESt and the voltage on St.
Positive power supply (5 V typ.).
No Connection.
16
19
PWDN
18-21
22
21-24
26
D0-D3
ESt
23
27
St/GT
24
8, 9
17
28
3, 5,
10,11
16, 20,
25
V
DD
NC
1.0
Functional Description
The MT8885 Integrated DTMF Transceiver consists of a high performance DTMF receiver with an internal gain
setting amplifier and a DTMF generator, which employs a burst counter to synthesize precise tone bursts and
pauses. A call progress mode can be selected so that frequencies within the specified passband can be detected.
The adaptive micro interface allows various microcontrollers to access the MT8885 internal registers.
1.1
Power-Down
The MT8885 provides enhanced power-down functionality to facilitate minimization of supply current consumption.
DTMF transmitter and receiver circuit blocks may be independently powered down via register control. When
asserted, the RxEN control bit powers down all analog and digital circuitry associated solely with the DTMF and
Call Progress receiver. The TOUT control bit is used to disable the transmitter and put all circuitry associated only
with the DTMF transmitter in power-down mode. With the TOUT control bit asserted, the TONE output pin is held in
a high impedance (floating) state. When both power-down control bits are asserted, circuits utilized by both the
DTMF transmitter and receiver are also powered down. This power-down control disables the crystal oscillators,
and the VRef generator. In addition, the IRQ, TONE output and DATA pins are held in a high impedance state.
Finally, the whole device is put in a power-down state when the PWDN pin is asserted.
3
Zarlink Semiconductor Inc.
ZARLINK [ ZARLINK SEMICONDUCTOR INC ]
