Advance Information

MT88L89

4-135

Table 7

Table 8

BIT

NAME

DESCRIPTION

b0

BURST

Burst Mode Select. A logic high de-activates burst mode; a logic low enables burst mode.

When activated, the digital code representing a DTMF signal (see Table 1) can be written

to the transmit register, which will result in a transmit DTMF tone burst and pause of equal

durations (typically 51 msec). Following the pause, the status register will be updated (b1 -

Transmit Data Register Empty), and an interrupt will occur if the interrupt mode has been

enabled.

When CP mode (control register A, b1) is enabled the normal tone burst and pause

durations are extended from a typical duration of 51 msec to 102 msec.

When BURST is high (de-activated) the transmit tone burst duration is determined by the

TOUT bit (control register A, b0).

b1

RxEN

This bit enables the DTMF and Call Progress Tone receivers. A logic low enables both

circuits. A logic high deactivates and puts both receiver circuits into power down mode.

b2

S/D

Single or Dual Tone Generation. A logic high selects the single tone output; a logic low

selects the dual tone (DTMF) output. The single tone generation function requires further

selection of either the row or column tones (low or high group) through the C/R bit (control

register B, b3).

b3

C/R

Column or Row Tone Select. A logic high selects a column tone output; a logic low selects

a row tone output. This function is used in conjunction with the S/D bit (control register B,

b2).

BIT

NAME

STATUS FLAG SET

STATUS FLAG CLEARED

b0

IRQ

Interrupt has occurred. Bit one

(b1) or bit two (b2) is set.

Interrupt is inactive. Cleared after

Status Register is read.

b1

TRANSMIT DATA

REGISTER EMPTY

(BURST MODE ONLY)

Pause duration has terminated

and transmitter is ready for new

data.

Cleared after Status Register is

read or when in non-burst mode.

b2

RECEIVE DATA REGISTER

FULL

Valid data is in the Receive Data

Register.

Cleared after Status Register is

read.

b3

DELAYED STEERING

Set upon the valid detection of

the absence of a DTMF signal.

Cleared upon the detection of a

valid DTMF signal.