Datasheet

214
4317K–AVR–03/2013
AT90PWM2/3/2B/3B
19.3.3 Manchester encoding
Manchester encoding (also know as Biphase Code) is a synchronous clock encoding technique
used to encode the clock and data of a synchronous bit stream. In this technique, the actual
binary data to be transmitted are not sent as a sequence of logic 1's and 0's as in level encoded
way as in standard USART (known technically as Non Return to Zero (NRZ)). Instead, the bits
are translated into a slightly different format that has a number of advantages over using straight
binary encoding (i.e. NRZ).
Manchester encoding follows the rules:
• If the original data is a Logic 1, the Manchester code is: 0 to 1 (upward transition at bit
center)
• If the original data is a Logic 0, the Manchester code is: 1 to 0 (downward transition at bit
center)
Figure 19-2. Manchester Bi-phase levels
19.3.3.1 Manchester frame
The USART supports Manchester encoded frames with the following characteristics:
• One start bit Manchester encoded (logical ‘1’)
• 5, 6, 7, 8, 9, 13, 14,15,16,17 data bits in transmission or reception (MSB or LSB first)
• The number of data bit in a frame is independently configurable in reception and
transmission mode.
• One or Two stop bits (level encoded)
Figure 19-3. Manchester Frame example
Logical 0 Logical 1
1 0 0 1 1 1 1 0 1 0 0 1 0 1 0 1 0
Start
Bit
Data Bits
(up to 17 data bit)
Stop
Bits
Encoder Clock
Manchester Data
Binary Data