Motorola ColdFire MCF5281 - Manual (Page 431)

UART Modules
Freescale Semiconductor 23-11
23.3.6 UART Receive Buffers (URBn)
The receive buffers 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 23-18 ). RB contains
the character in the receiver.
3–2
TC
Transmit command field. Selects a single transmit command.
1–0
RC
Receive command field. Selects a single receive command.
Table 23-7. 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.
MCF5282 and MCF5216 ColdFire Microcontroller User’s Manual, Rev. 3