Data Sheet

AS3588A

Rev. 3.1

Page 4 of 15

July 1999

quential addressing information. The count difference

between the bases is 32 which is two time slots, the

minimum PCM propagation time. The device activates

the output channels one bit time before input channels

are strobed. This feature allows inputs and outputs to

be tied together cancelling any analogue delay of

digital outputs up to a time which is specified in the

timing diagramme.

Serial Input PCM Conversion

Serial data at 2048 kbit/sec is received at the eight

PCM inputs INP PCM1 to INP PCM7. Each serial port

accepts 32 64 kbit channels of data, each channel

containing an 8-bit word which may represent a PCM-

encoded analogue/voice sample as provided by a

codec (e.g. AMS` S44231 to S44238 or AS3554 to

AS3569 codec family). This serial input word is con-

verted into parallel data by a serial to parallel PCM

converter.

Data Memory and Connection Memory

The parallel data is stored in the 256 x 8 Data Memory

which is updated every frame period. The locations in

the Data Memory are associated with particular chan-

nels in particular PCM input ports. The locations in the

256 x 9 Connection Memory are associated with par-

ticular PCM output streams. These locations can be

accessed by the microprocessor which controls the

device. When a channel is due to be transmitted on a

PCM output stream the data can either be switched

from a PCM input channel in space (INP PCM1 to

INP PCM7)) or time (slot 1 to 32). In this case the 9th

bit in the control memory is set to "0". Alternatively it

can originate from the Connection Memory. In this

case the 9th bit of the control memory is set to "1". If

the data is switched from an input, the contents of the

Connection Memory associated with the output chan-

nel is used to point to the Data Memory locations. This

Data Memory address corresponds to the channel of

the PCM input stream on which the data for switching

has arrived. If the data for the output channel

originates from the microprocessor then the contents

of the Connection Memory associated with the PCM

output Channel are output directly and this data is

output as message constantly once every frame until

the microprocessor intervenes.

Serial Output PCM Conversion

The parallel channel data is converted back into a se-

rial PCM stream by a parallel to serial PCM converter

and is transmitted at the eight PCM output ports OUT

PCM1 to OUT PCM7.

Microprocessor Interface

The asynchronous microprocessor interface is con-

trolled by 9 control signals (WR, RD, CS1, CS2, A1,

S1, A2, S2, DR) and provides data and instruction

transfer via the 8-bit data bus (D7 to D0). For each of

the six available operations two to four data bytes and

one instruction byte are written into a five level deep

stack. After a check of the correctness the function is

executed. Data bytes are defined by a low level on the

C/D input while a command byte is defined by a high

level. The active high Data Ready output pin of

AS3588

provides

a

handshake

signal

to

the

microprocessor when transfer information is ready.

During long instructions like an initialization routine

after RESET or execution of instruction 6 only valid

opcodes with the associated datafield are accepted;

the execution of the new instruction is started after the

current instruction has been completed. Memory con-

tent and status information can be extracted by read-

ing the two internal registers OR1 and OR2 and using

C/D as multiplexing control signal. OR1 is selected by

a low level on the C/D input and contains either data

from the data memory or the connection memory.

OR2 is selected with a high level and contains the op-

code and additional status information. Read opera-

tions are only executed if the device is fully selected

with CS1=CS2=0 and A1=S1 and A2=S2. There are

no restrictions on the sequence of read and write op-

erations as long as only one of the control pins (RD,

WR) is selected. If both pins are pulled low, the inter-

face bus goes into high impedance state. The register

contents is maintained as long as this condition per-

sists and is updated 3 cycles after a new opode or an

OR2 read. Single or multiple read operations of OR1

and OR2 should be carried out with separate read

strobes which are responsible of stepping through the

instruction flow.

Software Control

AS3588A performs two switching functions and four

auxiliary functions for diagnostic purposes and data in-

sertion from the microprocessor interface.

1) PCM CHANNEL CONNECTION

This function connects a PCM input channel to a PCM

output channel. The control information from the

microprocessor consists of four data bytes and one

command byte. Byte one and two contain information

about the PCM input line and PCM input channel that

is written into the connection memory. Byte three and

four contain information on the PCM output line and

the PCM output channel and act as address to the

specific connection memory location. If AS3588 is se-

lected by CS1=CS2=0 and if the condition A1=S1 and

A2=S2 is met, the command instruction is executed as

defined. If the device is selected by CS1 and CS2 only

this command will perform a disconnect function on

the specific output channel. If the instruction code was

found to be invalid, DR is driven low until a valid

instruction code is supplied; the registers are not

modified.

2) PCM CHANNEL DISCONNECTION

This function disconnects a PCM output channel. The

control information from the microprocessor consists