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Intel® PXA255 Processor Developer’s Manual 17-21
Hardware UART
17.5.12 Modem Control Register (MCR)
The MCR, shown in Table 17-16, uses the modem control pin nRTS to control the interface with a
modem or data set. The MCR also controls the loopback mode. Loopback mode must be enabled
before the UART is enabled.
This is a read/write register. Ignore reads from reserved bits. Write zeros to reserved bits.
3FE
FRAMING ERROR
FE indicates that the received character did not have a valid stop bit. FE is set when the bit
following the last data bit or parity bit is detected as 0. If the LCR had been set for two stop
bit mode, the receiver does not check for a valid second stop bit. The FE indicator is reset
when the processor reads the LSR. The UART re-synchronizes after a framing error. To do
this it assumes that the framing error was due to the next start bit, so it samples this “start”
bit twice and then reads in the “data”. In FIFO mode, FE shows a framing error for the
character at the front of the FIFO, not for the most recently received character.
0 = No framing error
1 = Invalid stop bit has been detected
2PE
PARITY ERROR
Indicates that the received data character does not have the correct even or odd parity, as
selected by the even parity select bit. PE is set when a parity error is detected and is
cleared when the processor reads the LSR. In FIFO mode, PE shows a parity error for the
character at the front of the FIFO, not the most recently received character.
0 = No parity error
1 = Parity error has occurred
1OE
OVERRUN ERROR
In non-FIFO mode, OE indicates that data in the Receive Buffer register was not read by the
processor before the next character was received. The new character is lost. In FIFO mode,
OE indicates that all 64 bytes of the FIFO are full and the most recently received byte has
been discarded. The OE indicator is set when an overrun condition is detected and cleared
when the processor reads the LSR.
0 = No data has been lost
1 = Received data has been lost
0DR
DATA READY
DR is set when a complete incoming character has been received and transferred into the
Receive Buffer register or the FIFO. In non-FIFO mode, DR is cleared when the receive
buffer is read. In FIFO mode, DR is cleared if the FIFO is empty (last character has been
read from Receive Buffer register) or the FIFO is reset with FCR[RESETRF].
0 = No data has been received
1 = Data is available in RBR or the FIFO
Table 17-15. LSR Bit Definitions (Sheet 2 of 2)
Physical Address
0x4160_0014
Line Status Register (LSR) PXA255 Processor Hardware UART
Bit
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
reserved
FIFOE
TEMT
TDRQ
BI
FE
PE
OE
DR
Reset ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 0 1 1 0 0 0 0 0
Bits Name Description