Datasheet

SAM9261 [DATASHEET]
Atmel-6062O-ATARM-SAM9261-Datasheet_21-Jun-16
442
31.6.3.5 Parity
The USART supports five parity modes selected by programming the PAR field in the Mode Register (US_MR).
The PAR field also enables the Multidrop mode, see “Multidrop Mode” on page 443. 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 at 0 if a number of 1s in the
character data bit is even, and at 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 at 1 if a number of 1s in the character data bit
is even, and at 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 at 1 for all characters. The receiver parity checker reports an error
if the parity bit is sampled at 0. If the space parity is used, the parity generator of the transmitter drives the parity bit
at 0 for all characters. The receiver parity checker reports an error if the parity bit is sampled at 1. If parity is
disabled, the transmitter does not generate any parity bit and the receiver does not report any parity error.
Table 31-6 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 at 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 Channel Status Register
(US_CSR). The PARE bit can be cleared by writing the Control Register (US_CR) with the RSTSTA bit at 1. Figure
31-12 illustrates the parity bit status setting and clearing.
Figure 31-12. Parity Error
Table 31-6. 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
D0 D1 D2 D3 D4 D5 D6 D7
RXD
Start
Bit
Bad
Parity
Bit
Stop
Bit
Baud Rate
Clock
Write
US_CR
PARE
RXRDY
RSTSTA = 1