PCD6003 datasheet(66/96 Pages) PHILIPS

66 / 96 page

2001 Apr 17

Philips Semiconductors

Product speciﬁcation

Digital telephone answering machine chip

PCD6003

15 IOM

15.1

Features

The IOM block in the PCD6003 is a 4-wire serial interface

performing following functions:

• Digital interface with up to two 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

speech CODEC ICs

• Autonomous storing/fetching of data into/from the

DSP I/O registers

• Byte or word (16 bits) transfer.

15.2

Pin description

The following pins are used by the IOM interface:

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

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

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

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

• FSC: 8 kHz frame synchronization input/output

• DCK: data clock input/output. Twice the data

transmission frequency on DI and DO, except in the

non-doubled data clock mode (see Section 15.3).

These pins are alternative functions of P3. When

activated, 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

and DCK are inputs or push-pull outputs, depending on the

IOM being in Slave or Master mode. Activation of the IOM

alternative functions of P3 and switching between Slave or

Master mode is controlled by the SFR ALTP, bit 6 and 5

respectively (see Section 16.2 for more details).

15.3

Functional description

The digital interface of the PCD6003 can work at several

bit rates, summarized in Table 61. A particular bit rate is

selected by writing the 3-bit code given in the first column

of the table into the IOM control register bits IOMC[15:13].

Choosing the code ‘000’ or ‘001’ deactivates the IOM

interface and stops all the transactions on the IOM bus.

This is the default state after reset.

The PCD6003 IOM can be master or slave. After reset the

IOM is in Slave mode. Switching between Slave or Master

mode is controlled by the SFR ALTP, bit 6 and bit 5

respectively (see Section 16.2.5 for more details). In Slave

mode both FSC and DCK are inputs. In Master mode both

FSC and DCK are outputs. In Master mode FSC and DCK

are generated by the TICB (see Section 9.1). Master mode

should only be used in combination with the bit rate

768 kbits/s. Slave mode should only be used when

operating with a 3.456 MHz (or multiple) crystal.

In general, proper IOM functionality is only guaranteed

at DSP operating frequencies of 28 and 42 MHz.

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.

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

data rate in IOM mode. In speech mode, the

DCK 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 two IOM data buffers, allowing the use of two

8-bit channel. One channel is 64 kbits/s in case of 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 15.6 for

timing information.

15.4

IOM data buffers

Table 58 and 59 show the two 16-bit DSP registers used

as data buffers: IOMDI for storing inbound data and

IOMDO for the outbound data. The high bytes store the

data of buffer 1, the low bytes the data of buffer 0.

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