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UART Modules
MCF52211 ColdFire® Integrated Microcontroller Reference Manual, Rev. 2
Freescale Semiconductor 24-11
24.3.6 UART Receive Buffers (URBn)
The receive buffers (shown in Figure 24-8) contain one serial shift register and three receiver holding
registers, which act as a FIFO. URXDn is connected to the serial shift register. The CPU reads from the
top of the FIFO while the receiver shifts and updates from the bottom when the shift register is full (see
Figure 24-18). RB contains the character in the receiver.
3–2
TC
TC Field (This field selects a single command)
1–0
RC
RC (This field selects a single command)
Table 24-7. UCRn Field Descriptions (continued)
Field Description
Command Description
00
NO ACTION TAKEN Causes the transmitter to stay in its current mode: if the transmitter is enabled, it
remains enabled; if the transmitter is disabled, it remains disabled.
01 TRANSMITTER
ENABLE
Enables operation of the UART’s transmitter. USRn[TXEMP,TXRDY] are set. If the
transmitter is already enabled, this command has no effect.
10
TRANSMITTER
DISABLE
Terminates transmitter operation and clears USRn[TXEMP,TXRDY]. If a character
is being sent when the transmitter is disabled, transmission completes before the
transmitter becomes inactive. If the transmitter is already disabled, the command
has no effect.
11 — Reserved, do not use.
Command Description
00
NO ACTION TAKEN Causes the receiver to stay in its current mode. If the receiver is enabled, it
remains enabled; if disabled, it remains disabled.
01 RECEIVER ENABLE If the UART module is not in multidrop mode (UMR1n[PM] ≠ 11), RECEIVER ENABLE
enables the UART's receiver and forces it into search-for-start-bit state. If the
receiver is already enabled, this command has no effect.
10
RECEIVER DISABLE Disables the receiver immediately. Any character being received is lost. The
command does not affect receiver status bits or other control registers. If the
UART module is programmed for local loopback or multidrop mode, the receiver
operates even though this command is selected. If the receiver is already
disabled, the command has no effect.
11 — Reserved, do not use.