
15-18
MCF5249UM
MOTOROLA
Register Description and Programming
15.4.1.3
Status Registers (USRn)
The USR registers indicate the status of the characters in the receive FIFO and the status of the
transmitter and receiver. The RB, FE, and PE bits are cleared by the Reset Error Status command in the
UCR registers if the RB bit has not been read. Also, RB, FE, PE and OE can also be cleared by reading
the Receive buffer (URB).
Table 15-8 Status Registers (USR0 and USR1)
BITS
7
6
5
4
3
2
1
0
FIELD
RB
FE
PE
OE
TXEMP
TXRDY
FFULL
RXRDY
RESET
0
00
0
R/W
READ/WRITE SUPERVISOR OR USER
ADDR
MBAR + $1C4 (USR0)
MBAR + $204 (USR1)
Table 15-9 Status Bit Descriptions
BIT NAME
DESCRIPTION
RB
Received Break
1 = An all-zero character of the programmed length has been received without a stop bit.
The RB bit is valid only when the RxRDY bit is set. A single FIFO position is occupied when
a break is received. Additional entries into the FIFO are inhibited until RxD returns to the high
state for at least one-half bit time, which is equal to two successive edges of the internal or
external clock x 1 or 16 successive edges of the external clock x 16. The received break
circuit detects breaks that originate in the middle of a received character. However, if a break
begins in the middle of a character, it must persist until the end of the next detected
character time.
0 = No break has been received.
FE
Framing Error
1 = A stop bit was not detected when the corresponding data character in the FIFO was
received. The stop-bit check occurs in the middle of the first stop-bit position. The bit is valid
only when the RxRDY bit is set.
0 = No framing error has occurred.
PE
Parity Error
1 = When the with-parity or force-parity mode is programmed in the UMR1, the
corresponding character in the FIFO was received with incorrect parity. When the multidrop
mode is programmed, this bit stores the received A/D bit. This bit is valid only when the
RxRDY bit is set.
0 = No parity error has occurred.
OE
Overrun Error
1 = One or more characters in the received data stream have been lost. This bit is set on
receipt of a new character when the FIFO is full and a character is already in the shift register
waiting for an empty FIFO position. When this occurs, the character in the receiver-shift
register and its break-detect, framing-error status, and parity error, if any, are lost. The
reset-error status command in the UCR clears this bit.
0 = No overrun has occurred.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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