TP3155N datasheet(5/10 Pages) NSC

5 / 10 page

Functional Description

OPERATING MODES

The TP3155 control interface requires an 8-bit serial control

word which is compatible with the TP3020TP3021 and

29102911 CODECs Two bits X and R define which of the

two groups of frame sync outputs FSX0toFSX3orFSR0to

FSR3 is affected by the control word and a 6-bit assign-

ment field specifies the selected time slot from 0 to 31 A

frame sync output is active-high for one time slot which is

always 8 cycles of BCLK A frame may consist of any num-

ber of time slots up to 32 If a timeslot is assigned which is

beyond the number of time slots in a frame the FSX or FSR

output to which it was assigned will remain inactive

Two modes of operation are available Mode 1 is for sys-

tems requiring different time slot assignments for the trans-

mit and receive direction of each channel Mode 1 is select-

ed by leaving pin 9 (MODE) open-circuit or connecting it to

VCC In this case Pin 13 is the RSYNC input which defines

the start of each receive frame and the four outputs

FSR0–FSR3 are assigned with respect to RSYNC The

XSYNC input defines the start of each transmit frame and

outputs FSX0–FSX3 are assigned with respect to XSYNC

XSYNC may have any phase relationship with RSYNC In-

puts CH0 and CH1 select the channel from 0 to 3 (see

Table Ia)

Mode 2 provides the option of assigning all 8 frame sync

outputs with respect to the XSYNC input Mode 2 is select-

ed by connecting pin 9 (MODE) to GND This makes the

TP3155 TSAC useful for either an 8-channel undirectional

controller or for systems in which the transmit and receive

directions of each channel are always assigned to the same

time slot as the other ie the FSX and FSR inputs on the

COMBO CODECFilter are hard-wired together In this

case logical selection of the channel to be assigned is

made via inputs CH0 CH1 and CH2 (see Table Ib)

POWER-UP INITIALIZATION

During power-up all frame sync outputs FSX0–FSX3 and

FSR0–FSR3 are inhibited and held low No outputs will go

active until a valid time slot assignment is made

LOADING CONTROL DATA

During the loading of control data the binary code for the

selected channel must be set on inputs CH0 and CH1 (and

CH2 in mode 2) see Tables Ia and Ib

Control data is clocked into the DC input on the falling

edges of CLKC while CS is low

A new time slot assignment is transferred to the selected

assignment register on the high going transition of CS The

new assignment is re-synchronized to the system clock

such that the new FS output pulses will start at the next

complete valid time slot after the rising edge of CS

TIME SLOT COUNTER OPERATION

At the start of TS0 of each transmit frame defined by the

first falling edge of BCLK after XSYNC goes high the trans-

mit time slot counter is reset to 000000 and begins to incre-

ment once every 8 cycles of BCLK Each count is compared

with the 4 transmit assignment registers and on finding a

match a frame sync pulse is generated at that FSX output

Similarly the first falling edge of BCLK after RSYNC goes

high defines the start of receive TS0

and outputs

FSR0–FSR3 are generated with respect to TS0 when the

receive time slot counter matches the appropriate receive

assignment register

TSX OUTPUT

In mode 1 (separate transmit and receive assignments) this

output pulls low whenever any FSX output pulse is being

generated In mode 2 this output pulls low whenever any

FSX or FSR output is being generated At all other times it is

open-circuit allowing the TSX outputs of a number of

TSACS to be wire-ANDed together with a common pull-up

resistor This signal can be used to control the TRI-STATE

enable input of a line driver to buffer the transmit PCM bus

from the CODECFilters to the backplane

TABLE Ia Control Mode 1

(TP3020TP3021 Compatible)

X is the first bit clocked into the DC input

Control Data Format

Time Slot

000000

000001

000010

011110

011111

(Note 1)

CH1

CH0

Channel Selected

Assign to FSx0 andor FSR0

Assign to FSx1 andor FSR1

Assign to FSx2 andor FSR2

Assign to FSx3 andor FSR3

Action

Assign time slot to both selected FSX and FSR

Assign time slot to selected FSX only

Assign time slot to selected FSR only

Disable both selected FSX and FSR

TABLE Ib Control Mode 2

CH2

CH1

CH0

Channel Selected

Assign to FSX0

Assign to FSX1

Assign to FSX2

Assign to FSX3

Assign to FSR0

Assign to FSR1

Assign to FSR2

Assign to FSR3

Action

Assign time slot to selected output

(

Disable selected output

Note 1

When T5 e 1 then the appropriate FSX or FSR output is inactive

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