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UART Modules
MCF5213 ColdFire® Integrated Microcontroller Reference Manual, Rev. 3
Freescale Semiconductor
21-7
21.3.3
UART Status Registers (USR
n
)
The USR
n
registers, shown in
, show the status of the transmitter, the receiver, and the FIFO.
Table 21-4. UMR2
n
Field Descriptions
Field
Description
7–6
CM
Channel mode. Selects a channel mode.
Section 21.4.3, “Looping Modes
,” describes individual modes.
00 Normal
01 Automatic echo
10 Local loop-back
11 Remote loop-back
5
TXRTS
Transmitter ready-to-send. Controls negation of U
n
RTS to automatically terminate a message transmission.
Attempting to program a receiver and transmitter in the same UART for U
n
RTS control is not permitted and disables
U
n
RTS control for both.
0 The transmitter has no effect on U
n
RTS.
1 In applications where the transmitter is disabled after transmission completes, setting this bit automatically clears
UOP[RTS] one bit time after any characters in the transmitter shift and holding registers are completely sent,
including the programmed number of stop bits.
4
TXCTS
Transmitter clear-to-send. If TXCTS and TXRTS are set, TXCTS controls the operation of the transmitter.
0 U
n
CTS has no effect on the transmitter.
1 Enables clear-to-send operation. The transmitter checks the state of U
n
CTS each time it is ready to send a
character. If U
n
CTS is asserted, the character is sent; if it is deasserted, the signal U
n
TXD remains in the high
state and transmission is delayed until U
n
CTS is asserted. Changes in U
n
CTS as a character is being sent do
not affect its transmission.
3–0
SB
Stop-bit length control. Selects length of stop bit appended to the transmitted character. Stop-bit lengths of 9/16 to
2 bits are programmable for 6–8 bit characters. Lengths of 1-1/16 to 2 bits are programmable for 5-bit characters. In
all cases, the receiver checks only for a high condition at the center of the first stop-bit position, one bit time after the
last data bit or after the parity bit, if parity is enabled. If an external 1x clock is used for the transmitter, clearing bit 3
selects one stop bit and setting bit 3 selects two stop bits for transmission.
SB
5 Bits
6–8 Bits
SB
5–8 Bits
0000
1.063
0.563
1000
1.563
0001
1.125
0.625
1001
1.625
0010
1.188
0.688
1010
1.688
0011
1.250
0.750
1011
1.750
0100
1.313
0.813
1100
1.813
0101
1.375
0.875
1101
1.875
0110
1.438
0.938
1110
1.938
0111
1.500
1.000
1111
2.000