ATSAM3X4EA-AU Atmel, ATSAM3X4EA-AU Datasheet - Page 758
ATSAM3X4EA-AU
Manufacturer Part Number
ATSAM3X4EA-AU
Description
ARM Microcontrollers - MCU QFP144,GREEN, IND TEMP, MRL A
Manufacturer
Atmel
Datasheet
1.ATSAM3X8EA-AU.pdf
(1467 pages)
Specifications of ATSAM3X4EA-AU
Rohs
yes
Core
ARM Cortex M3
Processor Series
SAM3X
Data Bus Width
32 bit
Maximum Clock Frequency
84 MHz
Program Memory Size
256 KB
Data Ram Size
64 KB
On-chip Adc
Yes
Operating Supply Voltage
2.4 V to 3.6 V
Operating Temperature Range
- 40 C to +85 C
Package / Case
LQFP-144
Mounting Style
SMD/SMT
Factory Pack Quantity
60
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35.5.2.2
35.5.2.3
758
758
SAM3X/A
SAM3X/A
Start Detection and Data Sampling
Receiver Ready
The programmer can also put the receiver in its reset state by writing UART_CR with the bit
RSTRX at 1. In doing so, the receiver immediately stops its current operations and is disabled,
whatever its current state. If RSTRX is applied when data is being processed, this data is lost.
The UART only supports asynchronous operations, and this affects only its receiver. The UART
receiver detects the start of a received character by sampling the URXD signal until it detects a
valid start bit. A low level (space) on URXD is interpreted as a valid start bit if it is detected for
more than 7 cycles of the sampling clock, which is 16 times the baud rate. Hence, a space that is
longer than 7/16 of the bit period is detected as a valid start bit. A space which is 7/16 of a bit
period or shorter is ignored and the receiver continues to wait for a valid start bit.
When a valid start bit has been detected, the receiver samples the URXD at the theoretical mid-
point of each bit. It is assumed that each bit lasts 16 cycles of the sampling clock (1-bit period)
so the bit sampling point is eight cycles (0.5-bit period) after the start of the bit. The first sampling
point is therefore 24 cycles (1.5-bit periods) after the falling edge of the start bit was detected.
Each subsequent bit is sampled 16 cycles (1-bit period) after the previous one.
Figure 35-3. Start Bit Detection
Figure 35-4. Character Reception
When a complete character is received, it is transferred to the UART_RHR and the RXRDY sta-
tus bit in UART_SR (Status Register) is set. The bit RXRDY is automatically cleared when the
receive holding register UART_RHR is read.
Sampling Clock
Example: 8-bit, parity enabled 1 stop
Sampling
Baud Rate
URXD
URXD
Clock
0.5 bit
period
True Start Detection
period
1 bit
D0
D1
True Start
Detection
D2
D3
D4
D5
D6
D7
11057B–ATARM–28-May-12
11057B–ATARM–28-May-12
Parity Bit
Stop Bit
D0
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