at91sam9g20-cu ATMEL Corporation, at91sam9g20-cu Datasheet - Page 482

• Manufacturer Part Number: at91sam9g20-cu
• Description: At91 Arm Thumb Microcontrollers
• Manufacturer: ATMEL Corporation

Figure 32-26. Break Transmission
32.6.3.15
32.6.3.16
482
Baud Rate
TXEMPTY
US_CR
TXRDY
Clock
Write
TXD
AT91SAM9G20 Preliminary
Receive Break
Hardware Handshaking
Start
Bit
D0
D1
D2
STTBRK = 1
The transmitter considers the break as though it is a character, i.e. the STTBRK and STPBRK
commands are taken into account only if the TXRDY bit in US_CSR is at 1 and the start of the
break condition clears the TXRDY and TXEMPTY bits as if a character is processed.
Writing US_CR with the both STTBRK and STPBRK bits at 1 can lead to an unpredictable
result. All STPBRK commands requested without a previous STTBRK command are ignored. A
byte written into the Transmit Holding Register while a break is pending, but not started, is
ignored.
After the break condition, the transmitter returns the TXD line to 1 for a minimum of 12 bit times.
Thus, the transmitter ensures that the remote receiver detects correctly the end of break and the
start of the next character. If the timeguard is programmed with a value higher than 12, the TXD
line is held high for the timeguard period.
After holding the TXD line for this period, the transmitter resumes normal operations.
Figure 32-26
commands on the TXD line.
The receiver detects a break condition when all data, parity and stop bits are low. This corre-
sponds to detecting a framing error with data at 0x00, but FRAME remains low.
When the low stop bit is detected, the receiver asserts the RXBRK bit in US_CSR. This bit may
be cleared by writing the Control Register (US_CR) with the bit RSTSTA at 1.
An end of receive break is detected by a high level for at least 2/16 of a bit period in asynchro-
nous operating mode or one sample at high level in synchronous operating mode. The end of
break detection also asserts the RXBRK bit.
The USART features a hardware handshaking out-of-band flow control. The RTS and CTS pins
are used to connect with the remote device, as shown in
D3
D4
D5
D6
D7
illustrates the effect of both the Start Break (STTBRK) and Stop Break (STPBRK)
Parity
Bit
Stop
Bit
Break Transmission
STPBRK = 1
Figure
32-27.
End of Break
6384B–ATARM–15-Dec-08