
2001 Apr 17
46
Philips Semiconductors
Product specification
Digital telephone answering machine chip
PCD6001
10.12.4 M
ANCHESTER 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 W
AVEFORM 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 0.57V
DD
.
handbook, halfpage
MGM781
R0
WAVEFORM
GENERATOR
MOUT0
R1
MOUT1
VOUT
R2
MOUT2
C1
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
010
011
100
101
110
111
0
0.14V
DD
0.29V
DD
0.43V
DD
0.57V
DD
0.71V
DD
0.86V
DD
V
DD