HD9P6409-9 INTERSIL [Intersil Corporation], HD9P6409-9 Datasheet - Page 6

• Manufacturer Part Number: HD9P6409-9
• Description: CMOS Manchester Encoder-Decoder
• Manufacturer: INTERSIL [Intersil Corporation]

Manchester Code
Nonreturn-to-Zero (NRZ) code represents the binary values
logic-O and Iogic-1 with a static level maintained throughout
the data cell. In contrast, Manchester code represents data
with a level transition in the middle of the data cell. Manches-
ter has bandwidth, error detection, and synchronization
advantages over NRZ code.
The Manchester II code Bipolar One and Bipolar Zero shown
below are logical complements. The direction of the transi-
tion indicates the binary value of data. A logic-0 in Bipolar
One is defined as a Low to high transition in the middle of
the data cell, and a logic-1 as a high to low mid bit transition,
Manchester Il is also known as Biphase-L code.
The bandwidth of NRZ is from DC to the clock frequency fc/2,
while that of Manchester is from fc/2 to fc. Thus, Manchester
can be AC or transformer coupled, which has considerable
advantages over DC coupling. Also, the ratio of maximum to
minimum frequency of Manchester extends one octave, while
the ratio for NRZ is the range of 5-10 octaves. It is much eas-
ier to design a narrow band than a wideband amp.
Secondly, the mid bit transition in each data cell provides the
code with an effective error detection scheme. If noise pro-
duces a logic inversion in the data cell such that there is no
transition, an error indiction is given, and synchronization
must be re-established. This places relatively stringent
requirements on the incoming data.
Crystal Oscillator Mode
C1
C1
FIGURE 5. CRYSTAL OSCILLATOR MODE
C0
R1
16MHz
X1
O
C
BIPOLAR ZERO
I
X
BINARY CODE
BIPOLAR ONE
X
O
NONRETURN
C1 = 32pF
C0 = CRYSTAL + STRAY
X1 = AT CUT PARALLEL
R
R1 = 15M
BIT PERIOD
S
(TYP) = 30
TO ZERO
RESONANCE
FUNDAMENTAL
MODE
FIGURE 4. MANCHESTER CODE
HD-6409
1
0
5-6
2
1
The synchronization advantages of using the HD-6409 and
Manchester code are several fold. One is that Manchester is
a self clocking code. The clock in serial data communication
defines the position of each data cell. Non self clocking
codes, as NRZ, often require an extra clock wire or clock
track (in magnetic recording). Further, there can be a phase
variation between the clock and data track. Crosstalk
between the two may be a problem. In Manchester, the
serial data stream contains both the clock and the data, with
the position of the mid bit transition representing the clock,
and the direction of the transition representing data. There is
no phase variation between the clock and the data.
A second synchronization advantage is a result of the num-
ber of transitions in the data. The decoder resynchronizes on
each transition, or at least once every data cell. In contrast,
receivers using NRZ, which does not necessarily have tran-
sitions, must resynchronize on frame bit transitions, which
occur far less often, usually on a character basis. This more
frequent resynchronization eliminates the cumulative effect
of errors over successive data cells. A final synchronization
advantage concerns the HD-6409’s sync pulse used to ini-
tiate synchronization. This three bit wide pattern is suffi-
ciently distinct from Manchester data that a false start by the
receiver is unlikely.
LC Oscillator Mode
3
1
4
0
FIGURE 6. LC OSCILLATOR MODE
C1
C1
5
0
L
O
I
X
X
C E
C1 = 20pF
C0 = 5pF
f O
C1 2C0
------------------------- -
---------------------- -
2
–
1
2
LC e