PCD6003 datasheet(46/96 Pages) PHILIPS

46 / 96 page

2001 Apr 17

Philips Semiconductors

Product speciﬁcation

Digital telephone answering machine chip

PCD6003

10.12.4 MANCHESTER CODING OF DATA

The bits of the data byte written in MBUF are Manchester

encoded as shown in Fig.17. A logic 1 is coded as a

LOW-to-HIGH transition in the middle of a bitcell, a logic 0

is coded as a HIGH-to-LOW transition.The Manchester

encoded signal contains redundancy for early error

detection in received bits. A non-matching 1 and 0 or

0 and 1 pair indicates an error condition.The Manchester

encoded signal has a polarity change in each bitcell.

10.12.5 WAVEFORM GENERATION WITH MOUT[2:0]

The 3 digital output pins MOUT[2:0] should be used as an

input to a 3-bit external DAC. The signals can be

connected via external resistors R2, R1 and R0 to a

summation point and then be filtered with an external

capacitor C1. This 3-bit DAC is shown in Fig.17.

Table 46 gives the relationship between MOUT[2:0] and

the voltage VOUT.

Table 46 VOUT as a function of MOUT[2:0]; note 1

Note

1. Resistor values are shown in Fig.17.

Figure 18 shows the possible waveforms that are

produced by the waveform generator. The horizontal axis

shows the sample counter on which the waveform

changes its value. Each bit is built-up out of 2

× 40

samples (n

× 3.456 MHz crystal, CKCON.6 = 0) or 2 × 42

samples (3.58 MHz, CKCON.6 = 1). The vertical axis

shows the values of MOUT[2:0], forming the inputs of the

resistive DAC. The first half of the waveform is determined

by the previous and the current bit, whereas the second

half of the waveform is determined by the current and the

next bit to be transmitted. The count frequency of the

sample counter depends on the programmed baud rate.

If the transmitter is disabled with MTEN set to logic 0,

MOUT[2:0] is <111> to save power in the resistive DAC.

If the transmitter is enabled and no data is transmitted,

MOUT[2:0] has an idle value of <100>, which corresponds

to 0.57VDD.

handbook, halfpage

MGM781

WAVEFORM

GENERATOR

MOUT0

MOUT1

VOUT

MOUT2

10 nF

Fig.17 3-bit DAC with MOUT[2:0].

R0 = R

R1 = 0.48

× R

R2 = 0.25

× R

MOUT[2:0]

VOUT

000

001

0.14VDD

010

0.29VDD

011

0.43VDD

100

0.57VDD

101

0.71VDD

110

0.86VDD

111

VDD

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