AN2262 Motorola / Freescale Semiconductor, AN2262 Datasheet - Page 20

• Manufacturer Part Number: AN2262
• Description: Wireless HC08 Modem
• Manufacturer: Motorola / Freescale Semiconductor

AN2262/D
RF Transmission
20
For operation of the MC33493 transmitter chip it is necessary to control two
lines in the minimal configuration:
The basic principle of Manchester encoding is that each bit is divided into two
halves. The level in the first period is the same as in the original NRZ (non-
return to zero) stream while the level in the second period is inverted. In other
words, the line level is inverted in the middle of each bit interval.
Besides some disadvantages (e.g., doubled bandwidth) it brings several
advantages which are beneficial especially for low-cost systems.
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One named PLLEN serves as the on/off control of the complete
transmitter.
The second one is called TXDATA and it actually controls the output of
the transmitter (i.e., OOK (on-off keying) modulation). The Manchester
encoded data stream has to appear on this line to conform to the
specification of the MC33591/3 receiver. For Manchester encoding
operation see
First, the edge that appears in the middle of each bit can be used as a
source for recovery of the received data clock as ‘it is always there’. It
also helps in the decoding of the bit boundary.
Second, the DC-level of a Manchester encoded stream remains 0 (or
constant), thus independent of the data pattern. Such an attribute is
often helpful in systems where the DC level is not transferred through
the channel and doesn’t need to be recovered at the receiving side. This
is also used in the MC33591/3 receiver.
NRZ STREAM
MANCHESTER ENCODED STREAM
Figure 11. Manchester Encoding Explanation
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Wireless HC08 Modem
Figure
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MOTOROLA