mcf5272 Freescale Semiconductor, Inc, mcf5272 Datasheet - Page 371

• Manufacturer Part Number: mcf5272
• Description: Mcf5272 Coldfire Integrated Microprocessor User
• Manufacturer: Freescale Semiconductor, Inc

MOTOROLA
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.
Bits
Address
1–0
Reset
Field
R/W
Value
00
01
10
11
NO ACTION TAKEN
RECEIVER ENABLE
RECEIVER DISABLE
7
Command
Table 16-6. UCRn Field Descriptions (Continued)
—
Figure 16-7. UART Receiver Buffer (URBn)
Causes the receiver to stay in its current mode. If the receiver is enabled, it
remains enabled; if disabled, it remains disabled.
If the UART module is not in multidrop mode (UMR1n[PM] * 11),
ENABLE
If the receiver is already enabled, this command has no effect.
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.
Reserved, do not use.
RC (This field selects a single command)
Chapter 16. UART Modules
enables the channel's receiver and forces it into search-for-start-bit state.
MBAR + 0x10C,0x14C
0000_0000
Read only
RB
Description
Register Descriptions
RECEIVER
0
16-11