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Bits
Value
Command
1–0
00
NO ACTION TAKEN
01
RECEIVER ENABLE
10
RECEIVER DISABLE
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. 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 23-19). RB contains the character in the receiver.
7
Field
Reset
R/W
Address
23.3.7 UART Transmit Buffers (UTBn)
The transmit buffers consist of the transmitter holding register and the transmitter shift
register. The holding register accepts characters from the bus master if channel's
USRn[TxRDY] is set. A write to the transmit buffer clears USRn[TxRDY], inhibiting any
more characters until the shift register 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
transmit buffer when the channel's TxRDY = 0 and when the transmitter is disabled have
no effect on the transmit buffer.
MOTOROLA
Table 23-6. UCRn Field Descriptions (continued)
RC (This field selects a single command)
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),
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.
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.
IPSBAR + 0x20C(URB0), 0x24C(URB1), 0x28C(URB2)
Figure 23-7. UART Receive Buffer (URBn)
Chapter 23. UART Modules
Description
RB
1111_1111
Read only
Register Descriptions
RECEIVER ENABLE
0
23-11
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