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11.4.1 UART Receive Register (URX)
This read-only register contains received characters and status. After reset, if the
receiver is enabled (RXEN = 1), the CHAR RDY bit is zero until the first character is
received, and the remainder of the register contents are undefined. The RX register is
echoed to 16 word addresses in order to support unloading the FIFO with the load
register quadrant (ldq) instruction.
U0RX — UART0 Receive Register
U1RX — UART1 Receive Register
15
14
13
12
CHAR
OVR
FRM
R
ERR
RDY
RUN
ERR
W
RESET:
0
X
X
X
*n = 0, 1, . . ., 15
X = Undefined
CHARRDY — Character Ready
This read-only bit indicates whether the character in the RX DATA field and associ-
ated flags are valid and ready to be read by the host.
0 = Character in RX DATA field and associated flags are invalid
1 = Character in RX DATA field and associated flags valid and ready for reading
At reset, this bit is cleared to zero.
ERR — Error Detect
When set, this read-only bit indicates that the character present in the RX DATA field
has an error status. The error can be an OVRRUN, FRMERR, BRK or PRERR. This
bit is updated and valid for each received character.
0 = No error status detected
1 = Error status detected
At reset, this bit is cleared to zero.
OVRRUN — Receiver Overrun
When set, this read-only bit indicates that the receiver ignored data to prevent over-
writing the data in the FIFO. Under normal circumstances, this bit should never be
set. It indicates that the user's software is not keeping up with the incoming data rate.
This bit is updated and valid for each received character, and when set indicates that
some number of characters were lost following the character for which the flag is set.
0 = No FIFO overrun
1 = A FIFO overrun was detected
At reset, this bit is cleared to zero.
MMC2001
UNIVERSAL ASYNCHRONOUS RECEIVER/TRANSMITTER MODULE
REFERENCE MANUAL
Freescale Semiconductor, Inc.
11
10
9
8
PR
BRK
0
0
ERR
X
X
X
X
Figure 11-2 UART Receive Register
For More Information On This Product,
Go to: www.freescale.com
7
6
5
4
RX DATA
X
X
X
X
10009000
1000A000
3
2
1
0
X
X
X
X
MOTOROLA
11-7
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