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PCD5096

Universal codec

Philips Electronics 

Philips Semiconductors

Universal codec

Preliminary specification

PCD5096

9 IOM

9.1 Features

The IOM block in the PCD5096 is a 4-wire serial interface

performing the following functions:

• Digital interface with up to fourteen 64 kbits/s channels

at a bit rate of n × 256 kbits/s (n = 1, 2, 3, 4 or 8),

complying with the IOM-2 specifications (IOM-2 is a

registered trademark of Siemens AG)

• Digital interface with 32 slots/frame and non-doubled

data clock, compatible with the digital interface of some

DTAM speech compression ICs

• Autonomous storing/fetching of data to/from the system

data memory (SDR) using internal addressing logic

• Byte or word (16 bits) transfer

• 14 data buffers (byte or word)

• Muting of speech data

• Local call.

9.2 Pin description

The following pins are used by the IOM-2 interface:

• DI: serial data input with a bit rate of n × 256 kbits/s

(n = 1, 2, 3, 4 or 8)

• DO: serial data output with a bit rate of n × 256 kbits/s

(n = 1, 2, 3, 4 or 8). DO is an open-drain pin, as many

devices must be able to write on the same data line in a

time-multiplexed mode. Therefore, DO must be

externally pulled-up.

• FSC: 8 kHz frame synchronization input

• DCL: data clock input. Twice the data transmission

frequency on DI and DO, except in the non-doubled data

clock mode (see Section 9.3).

9.3 Functional description

The digital interface of the PCD5096 can work at several

bit rates; these are specified Table 27. The bit rate is

selected by writing the appropriate 3 bit code, given in

Table 27, into Control Register 1 (address 79H).

The PCD5096 is always a slave on the IOM interface,

which means that both FSC and DCL are inputs. This is

valid for both the IOM modes and the Speech mode.

FSC is an 8 kHz framing signal for synchronizing data

transmission on DI and DO. The rising edge of FSC gives

the time reference for the first bit transmitted in the first slot

of a speech frame. The number of slots per speech frame

depends on the selected data rate. Each slot contains

8 data bits.

DCL is a data clock. Its frequency is twice the selected

data rate in IOM mode. In Speech mode, the DCL

frequency is equal to the data rate (2048 kHz for

2048 kbits/s).

DI is the serial data input. Data coming on DI in packets of

8 bits (A-law PCM encoded data) or 16 bits (linear PCM

data) is stored temporarily in an IOM data buffer, from

where it is processed by the on-chip DSP. On the other

hand, data written into the IOM data buffers by the DSP is

shifted out on pin DO.

There are 14 IOM data buffers, allowing the use of

14 different channels. One channel is 64 kbits/s for A-law

PCM encoded data and 128 kbits/s if linear PCM data is

transferred, in which case two consecutive slots are used.

The Speech mode was implemented to support the codec

interface of some speech compression ICs. This mode is

very similar to the IOM 32 slots mode, the main difference

being the non-doubled data clock. See Section 9.4 for

timing information.

Table 27 IOM modes

IOM2

0

0

0

0

1

1

1

IOM1

0

0

1

1

0

0

1

1

1

IOM0

0

1

0

1

0

1

0

1

MODE

These codes deactivate the IOM-2 interface and stop all the transactions on the

IOM bus. This is the default state after reset.

IOM slave mode, 256 kbits/s in 4 slots/speech-frame

IOM slave mode, 512 kbits/s in 8 slots/speech-frame

IOM slave mode, 768 kbits/s in 12 slots/speech-frame

IOM slave mode, 1024 kbits/s in 16 slots/speech-frame

Speech mode, 2048 kbits/s in 32 slots/speech-frame. The Speech mode is

similar to the IOM slave 32 slots mode, but with a non-doubled data clock DCL.

IOM slave mode, 2048 kbits/s in 32 slots/speech-frame

1997 Jan 22

20

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