M3488 datasheet(9/18 Pages) STMICROELECTRONICS

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GENERAL DESCRIPTION

The M3488 is intendedfor large telephoneswitching

systems, mainly central exchanges, digital line con-

centrators and private branch exchanges where a

distributed microcomputer control approach is ex-

tensively used. It consists of a speech memory

(SM), a control memory (CM), a serial/parallel and

a parallel/serial converter, an internal parallel bus,

an interface (8 data lines, 11 control signals) and

dedicated control logic.

By means of repeated clock division two timebases

are generated. These are preset from an external

synchronization signal to two specific count num-

bers so that sequential scanning of the bases give

synchronous addresses to the memories and I/O

channel controls. Different preset count numbers

are needed because of processing delays and

data path direction. The timebase for the input chan-

nels is delayed and the timebase for output chan-

nels is advanced with respect to the actual time.

Each serial PCM input channel is converted to par-

allel data and stored in the speech memory at the

beginning of any new time slot (according to first

timebase) in the location determined by input pin

number and time slot number. The control memory

CM maintains the correspondencesbetween input

and output channels. More exactly, for any output

pin/outputchannel combination the control memory

gives either the full address of the speech memory

location involved in the PCM transfer or an 8-bit

word to be supplied to the parallel/serial output con-

verter. A 9

th bit at each CM location defines the data

source for output links, low for SM, high for CM.

The late timebase is used to scan the output chan-

nels and to determine the pins to be serviced within

each channel ; enough idle cycles are left to the mi-

croprocessor for asynchronousinstruction process-

ing.

Two 8-bit registers OR1 and OR2 supply feedback

data for control or diagnosticpurposes ; OR1 comes

from internal bus i.e. from memories, OR2 gives an

opcode copy and additional data to the microcom-

puter. A four byte-five bit stack register and an in-

struction register, under microcomputer control,

store input data available at the interface.

Dedicated logic, under control of the microprocessor

interface, extracts the 0 channel content of any se-

lected PCM input bus, using spare cycles of SM.

M3488

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