PCD6003 datasheet(45/96 Pages) PHILIPS

45 / 96 page

2001 Apr 17

Philips Semiconductors

Product speciﬁcation

Digital telephone answering machine chip

PCD6003

10.12.3 DATA RECEPTION

A message is received as a block of one or more data

bytes. When enabled, the receiver starts sampling MIN

and tries to detect a Manchester pattern. As soon as

3 consecutive Manchester bits are detected the receiver

clock is locked (MRL = 1) and the receiver starts scanning

the incoming data for the programmed Manchester

preamble pattern. When the modem recognizes the

preamble pattern, bit MRP is set to logic 1. If a

non-Manchester bit is detected before finding the

preamble pattern then MRL is reset and MRE is set to

logic 1. The synchronization process has to restart. If the

preamble pattern has been detected the receiver starts to

Manchester decode the incoming data bits and shifts them

into an internal register. After eight bits the contents of the

internal register are copied to MBUF and MRF bit is set to

logic 1. The received byte can be read from MBUF while

receiving continues in the internal register. If a

non-Manchester bit is received during data reception then

MRE is set to logic 1 and MRL and MRP are reset. The

receiver has to resynchronize before receiving new data.

Whenever one of the bits MRF, MRE, MRP and MRL is set

the MRI bit is also set and an MRI interrupt is generated.

This means that when an MRI interrupt occurs the 4 status

bits have to be polled by software. The bit MRL allows the

software to decide very quickly whether an occupied

channel contains Manchester coded data or not. The MRP

bit is used to find the start of data transmission in a

message that is repeated over and over again. MRE is

used to detect a Manchester error, which is a violation of

the Manchester coding rule that the received level should

change in the middle of a bitcell. The MRF bit indicates that

the data in MBUF is ready to be read by the software.

During data reception the time between two settings of

MRF (each one generating an MRI interrupt) is;

Figure 16 shows an example of the timing diagram of data

reception.

baud rate

------------------------

handbook, full pagewidth

MGM780

data

non-Manchester

(speech)

non-Manchester

(speech)

read

MBUF

read

MBUF

clear

MRI

clear

MRI

clear

MRI

RX_MUTE should be

generated by microcontroller

upon interrupt

RX_MUTE should be

cleared by microcontroller

at end of message

write

MREN = 1

80C51

access

MIN

MRI

MRF

MRL

MRP

MRE

Fig.16 Data reception timing diagram.

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