Chapter 16. UART Modules
16-11
Register Descriptions
16.3.6 UART Receiver Buffers (URBn)
The receiver buffers contain one serial shift register and a 24-byte FIFO. RxD is connected
to the serial shift register. The CPU reads from the top of the stack while the receiver shifts
and updates from the bottom when the shift register is full (see Figure 16-24). RB contains
the character in the receiver.
16.3.7 UART Transmitter Buffers (UTBn)
The transmitter buffers consist of a 24-byte FIFO and the transmitter shift register. The
FIFO accepts characters from the bus master if the channel’s USRn[TxRDY] is set. A write
to the transmitter buffer clears TxRDY, inhibiting any more characters until the FIFO can
accept more data. When the shift register is empty, it checks if the holding register has a
valid character to be sent (TxRDY = 0). If there is a valid character, the shift register loads
it and sets USRn[TxRDY] again. Writes to the transmitter buffer have no effect when the
channel’s TxRDY = 0 and when the transmitter is disabled.
Figure 16-8 shows UTBn. TB contains the character in the transmitter buffer.
1–0
RC (This field selects a single command)
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 channel'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 loop-back 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.
7
0
Field
RB
Reset
0000_0000
R/W
Read only
Address
MBAR + 0x10C,0x14C
Figure 16-7. UART Receiver Buffer (URBn)
Table 16-6. UCRn Field Descriptions (Continued)
Bits
Value
Command
Description
Содержание DigitalDNA ColdFire MCF5272
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