AT91M40400 View Datasheet(PDF) - Atmel Corporation
Part Name
Description
MFG CO.
'AT91M40400' PDF : 116 Pages View PDF
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
(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
Idle state duration
between two characters
=
Time-guard
value
x
Bit
period
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.
Figure 39. Synchronous and Asynchronous Modes: Character Transmission
Example: 8-bit, parity enabled 1 stop
Baud Rate
Clock
TXD
Start D0 D1 D2 D3 D4 D5 D6 D7 Parity Stop
Bit
Bit Bit
68
AT91M40400
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