AT91M40400-25C ATMEL Corporation, AT91M40400-25C Datasheet - Page 68

• Manufacturer Part Number: AT91M40400-25C
• Description: 16/32-bit Microcontroller, 2.7V to 3.6V Operating Range
• Manufacturer: ATMEL Corporation

Transmitter
The transmitter has the same behavior in both synchronous
and asynchronous operating modes. Start bit, data bits,
parity bit and stop bits are serially shifted, lowest significant
bit first, on the falling edge of the serial clock. See example
in Figure 39.
The number of data bits is selected in the CHRL field in
US_MR.
The parity bit is set according to the PAR field in US_MR.
The number of stop bits is selected in the NBSTOP field in
US_MR.
When a character is written to US_THR (Transmit Holding),
it is transferred to the Shift Register as soon as it is empty.
When the transfer occurs, the TXRDY bit in US_CSR is set
until a new character is written to US_THR. If Transmit Shift
Register and US_THR are both empty, the TXEMPTY bit in
US_CSR is set.
Time-Guard
The Time-guard function allows the transmitter to insert an
idle state on the TXD line between two characters. The
duration of the idle state is programmed in US_TTGR
Figure 39. Synchronous and Asynchronous Modes: Character Transmission
68
Baud Rate
Example: 8-bit, parity enabled 1 stop
AT91M40400
Clock
TXD
Start
Bit
D0
D1
D2
D3
(Transmitter Time-Guard). When this register is set to zero,
no time-guard is generated. Otherwise, the transmitter
holds a high level on TXD after each transmitted byte dur-
ing the number of bit periods programmed in US_TTGR
Multi-Drop Mode
When the field PAR in US_MR equals 11X (binary value),
the USART is configured to run in Multi-drop mode. In this
case, the parity error bit PARE in US_CSR is set when data
is detected with a parity bit set to identify an address byte.
PARE is cleared with the Reset Status Bits Command
(RSTSTA) in US_CR. If the parity bit is detected low, identi-
fying a data byte, PARE is not set.
The transmitter sends an address byte (parity bit set) when
a Send Address Command (SENDA) is written to US_CR.
In this case, the next byte written to US_THR will be trans-
mitted as an address. After this any byte transmitted will
have the parity bit cleared.
between two characters
D4
Idle state duration
D5
D6
D7
Parity
Bit
=
Time-guard
Stop
Bit
value
x
period
Bit