Datasheet

443
32142D–06/2013
ATUC64/128/256L3/4U
The receiver will report parity errors in CSR.PARE, unless parity is disabled. Writing a one to
CR.RSTSTA will clear PARE. See Figure 20-10
Figure 20-10. Parity Error
20.6.3.6 Multidrop Mode
If PAR is either 0x6 or 0x7, the USART runs in Multidrop mode. This mode differentiates data
and address characters. Data has the parity bit zero and addresses have a one. By writing a one
to the Send Address bit (CR.SENDA) the user will cause the next character written to THR to be
transmitted as an address. Receiving a character with a one as parity bit will set PARE.
20.6.3.7 Transmitter Timeguard
The timeguard feature enables the USART to interface slow devices by inserting an idle state on
the TXD line in between two characters. This idle state corresponds to a long stop bit, whose
duration is selected by the Timeguard Value field in the Transmitter Timeguard Register
(TTGR.TG). The transmitter will hold the TXD line high for TG bit periods, in addition to the num-
ber of stop bits. As illustrated in Figure 20-11, the behavior of TXRDY and TXEMPTY is modified
when TG has a non-zero value. If a pending character has been written to THR, the TXRDY bit
will not be set until this characters start bit has been sent. TXEMPTY will remain low until the
timeguard transmission has completed.
Figure 20-11. Timeguard Operation
D0 D1 D2 D3 D4 D5 D6 D7
RXD
Start
Bit
Bad
Parity
Bit
Stop
Bit
Baud Rate
Clock
Write
CR
PARE
RXRDY
RSTSTA = 1
D0 D1 D2 D3 D4 D5 D6 D7
TXD
Start
Bit
Parity
Bit
Stop
Bit
Baud Rate
Clock
Start
Bit
TG = 4
Write
THR
D0 D1 D2 D3 D4 D5 D6 D7
Parity
Bit
Stop
Bit
TXRDY
TXEMPTY
TG = 4