121
AT94KAL Series FPSLIC
Rev. 1138G–FPSLI–11/03
Data Reception
Figure 65 shows a block diagram of the UART Receiver.
Figure 65.
UART Receiver
Note:
1. n = 0, 1
The receiver front-end logic samples the signal on the RXDn pin at a frequency 16 times the
baud-rate. While the line is idle, one single sample of logic 0 will be interpreted as the falling
edge of a start bit, and the start bit detection sequence is initiated. Let sample 1 denote the
first zero-sample. Following the 1-to-0 transition, the receiver samples the RXDn pin at sam-
ples 8, 9 and 10. If two or more of these three samples are found to be logic 1s, the start bit is
rejected as a noise spike and the receiver starts looking for the next 1-to-0 transition.
PE1/
PE3
DATA BUS
BAUD
UART I/O DATA
REGISTER (UDRn)
10(11)-BIT RX
SHIFT REGISTER
STORE UDRn
/16
BAUD x 16
RXENn
TXENn
CHR9n
RXB8n
TXB8n
U2Xn
RXCn
TXCn
UDREn
FEn
MPCMPn
ORn
UART CONTROL AND
STATUS REGISTER
(UCSRnB)
UART CONTROL AND
STATUS REGISTER
(UCSRnA)
RXCIEn
TXCIEn
UDRIEn
RXCn
DATA BUS
PIN CONTROL
LOGIC
BAUD RATE
GENERATOR
XTAL
RXCn
IRQ
DATA RECOVERY
LOGIC
RXDn