STLC3080 datasheet(14/23 Pages) STMICROELECTRONICS

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The flow-chart in Fig.A1 describes the sequence

of state machine supervising the STLC3080 op-

eration when the control is set for Active mode,

D0 D1 D2= 1 X X.

The state machine is a synchronous sequential

circuit internally clocked by a free running oscilla-

tor ; the ringing frequency applied at the CKRING

input is used to generate the

long time delay

WTIME=128xCKRING necessary for proper op-

eration as further described.

External control is supposed to be set for Active

mode :

D0 D1 D2= 1 X X.

OH-HI : line status flag , set High when Off-Hook

condition is detected in High Impedance Feeding;

it differs from OHK because it’s sensitive to the

longitudinal current.

OHK: line status flag , set High when Off-Hook

condition is detected in Stand-By or in Active

mode; it differs from OH-HI for its immunity to lon-

gitudinal current .

DLY: time-out flag, it is set High to resume, with

a given delay, the High Impedance Feeding when

an On-Hook condition (OHK=Low) is detected in

Stand-By or Active state.

1) Note that in this section the word ”mode” has

been used to indicate the operating status set

with D0, D1 and D2 pin: the word ”state” has

been used to indicate an internal status of the

finite state machine.

Flow-chart Description

H) A Reset condition, generated at Power On or

setting RES pin Low,

forces a Power-Down

condition.

A) High Impedance Feeding is entered after the

Active mode word is set and its maintained un-

til

an Off-Hook condition is detected (OH-

HI=High) ; in this case Stand-By state entered.

B) Stand-By state is set

to perform a validity

check of the Off-Hook status of the line before

entering

Active

state.

confirmed

(OH=High),

immediately Active state is en-

tered.

If not , Stand-By state remains set for a time

period WTIME generated through a counter

that times out after 128 x CKRING ; DLY=High

signals the state machine the time out to re-

sume the High Impedance Feeding.

An OHK = High detected during WTIME will im-

mediately enter Active state.

C) Active state is set for conversation

and

DET=Low signals to the controller the Off-Hook

condition of the line.

The status remains set as long as OHK=High

(Off-Hook).

D) When OHK=Low is detected (On Hook), DET

is immediately set High whereas Active state is

maintained for the period WTIME; when it ex-

pires

DLY is set High and High Impedance

Feeding is resumed.

If, during WTIME, OHK=High is detected Off

Hook), the state is returned to C) , i.e. Active

with DET=Low.

E) Ringing mode is set when D0 = D1 = 0 and D2 = 1.

After ring trip detection the SLIC is automat-

ically set in Active state (reverse or normal po-

larity according to D2 value set before ringing

mode). Ring trip detection is indicated by DET

pin: when it happens the SW must remove the

ringing mode word (001) and set the Active

mode word (100).

F) On-Hook Tx mode is selected when D0 = 0,

D1 = 1 and D2 = X.

After Off Hook detection the SLIC is automat-

ically set in Active state.

APPENDIX A

STLC3080

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