atmega163l ATMEL Corporation, atmega163l Datasheet - Page 72

• Manufacturer Part Number: atmega163l
• Description: Atmega163 8-bit Avr Microcontroller With 16k Bytes Of In-system Programmable Flash
• Manufacturer: ATMEL Corporation

Data Reception
Figure 46 shows a block diagram of the UART Receiver
Figure 46. UART Receiver
The Receiver front-end logic samples the signal on the RXD pin at a frequency 16 times
the baud rate. While the line is idle, one single sample of logical zero will be interpreted
as the falling edge of a start bit, and the start bit detection sequence is initiated. Let sam-
ple 1 denote the first zero-sample. Following the 1 to 0-transition, the receiver samples
the RXD pin at samples 8, 9, and 10. If two or more of these three samples are found to
be logical ones, the start bit is rejected as a noise spike and the receiver starts looking
for the next 1 to 0-transition.
If however, a valid start bit is detected, sampling of the data bits following the start bit is
performed. These bits are also sampled at samples 8, 9, and 10. The logical value found
in at least two of the three samples is taken as the bit value. All bits are shifted into the
Transmitter Shift Register as they are sampled. Sampling of an incoming character is
shown in Figure 47. Note that the description above is not valid when the UART trans-
mission speed is doubled. See “Double Speed Transmission” on page 78 for a detailed
description.
ATmega163(L)
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1142E–AVR–02/03