PCD6001 datasheet(44/96 Pages) PHILIPS

44 / 96 page

2001 Apr 17

Philips Semiconductors

Product speciﬁcation

Digital telephone answering machine chip

PCD6001

10.12.2 DATA TRANSMISSION

Data transmission is enabled if bit MTEN in register MCON

is set to logic 1. If MTEN is logic 0 data transmission is

disabled and MOUT[2:0] is set to <111> to zero the

currents in the resistive DAC. Setting MTEN to logic 1 sets

MOUT[2:0] to the Idle value <100>. This results in a value

close to 0.5VDD on the output signal of the external DAC.

Transmission is started by loading the first byte into

MSB.

A message is transferred in a block of 3 or more bytes, the

first two bytes being the programmed Manchester

preamble pattern. In order to insert the preamble pattern,

the first two bytes AAH and AxH (with x being the

MPR[3:0] values programmed in the receiver MSK

modem) have to be written to MBUF by software. After

this, the first byte of the message is written to MBUF.

As soon as MBUF is ready to accept new input, signal MTI

is set. A new byte written to MBUF automatically clears

MTI. The time between two MTI interrupts is:

(e.g. for 1200 baud, T = 6.7 ms).

If no new byte is written to MBUF at the end of a byte

transmission, the modem transmitter stops transmission

and MOUT[2:0] is set to the Idle state <100>. In this case

MTI must be cleared explicitly. If MTEN is reset during

transmission, the transmitter will finish the transmission of

the current byte and then will set MOUT[2:0] to the off state

<111>. No interrupt on MTI will be generated at the end of

the transmission.

During reception, a digital PLL re-synchronizes on the

active transition of every bit. This allows a continuous

transmission of long messages. Figure 15 shows a

possible timing diagram of data transmission.

baud rate

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

handbook, full pagewidth

MGM779

data ADH

data AAH

data 55H

write

MBUF

55H

write

MBUF

55H

80C51

access

MOUT

MTI

TX_MUTE

set

MTEN

clear

MTI

write

MBUF

AAH

write

MBUF

AAH

write

MBUF

ADH

Fig.15 Data transmission timing diagram.

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