Datasheet

763
SAM4S Series [DATASHEET]
11100F–ATARM–29-Jan-14
Figure 36-21. Receiver Status
36.7.3.8 Parity
The USART supports five parity modes that are selected by writing to the PAR field in the US_MR. The PAR field also
enables the multidrop mode, see “Multidrop Mode” on page 764. Even and odd parity bit generation and error detection
are supported.
If even parity is selected, the parity generator of the transmitter drives the parity bit to 0 if a number of 1s in the character
data bit is even, and to 1 if the number of 1s is odd. Accordingly, the receiver parity checker counts the number of
received 1s and reports a parity error if the sampled parity bit does not correspond. If odd parity is selected, the parity
generator of the transmitter drives the parity bit to 1 if a number of 1s in the character data bit is even, and to 0 if the
number of 1s is odd. Accordingly, the receiver parity checker counts the number of received 1s and reports a parity error
if the sampled parity bit does not correspond. If the mark parity is used, the parity generator of the transmitter drives the
parity bit to 1 for all characters. The receiver parity checker reports an error if the parity bit is sampled to 0. If the space
parity is used, the parity generator of the transmitter drives the parity bit to 0 for all characters. The receiver parity
checker reports an error if the parity bit is sampled to 1. If parity is disabled, the transmitter does not generate any parity
bit and the receiver does not report any parity error.
Table 36-9 shows an example of the parity bit for the character 0x41 (character ASCII “A”) depending on the
configuration of the USART. Because there are two bits to 1, 1 bit is added when a parity is odd, or 0 is added when a
parity is even.
When the receiver detects a parity error, it sets the PARE (Parity Error) bit in the US_CSR. The PARE bit can be cleared
by writing the US_CR with the RSTSTA bit to 1. Figure 36-22 illustrates the parity bit status setting and clearing.
D0 D1 D2 D3 D4 D5 D6 D7
RXD
Start
Bit
Parity
Bit
Stop
Bit
Baud Rate
Clock
Write
US_CR
RXRDY
OVRE
D0 D1 D2 D3 D4 D5 D6 D7
Start
Bit
Parity
Bit
Stop
Bit
RSTSTA = 1
Read
US_RHR
Table 36-9. Parity Bit Examples
Character Hexadecimal Binary Parity Bit Parity Mode
A 0x41 0100 0001 1 Odd
A 0x41 0100 0001 0 Even
A 0x41 0100 0001 1 Mark
A 0x41 0100 0001 0 Space
A 0x41 0100 0001 None None