MMUART Peripherals
UG0331 User Guide Revision 15.0
491
The following tables provide the register bit descriptions in detail.
13.4.1
Receiver Buffer Register (RBR)
13.4.2
Transmit Holding Register (THR)
13.4.3
FIFO Control Register (FCR)
Rx and Tx FIFOs are 16 bytes deep.
Table 468 •
RBR
Bit
Number
Name
R/W
Reset
Value
Description
[7:0]
RBR
R
N/A
This register holds the receive data bits for MMUART_x. The default value is
unknown since the register is loaded with data in the receive FIFO. Bit 0 is the
LSB and it is the first bit received. It may be configured as the MSB by
configuring the E_MSB_RX bit in the MM1. The divisor latch access bit
(DLAB), bit 7 of LCR, must be 0 to read this register. This register is read only.
Writing to this register with the DLAB 0 changes the transmit holding register
(
) register value.
Table 469 •
THR
Bit
Number
Name
R/W
Reset
Value
Description
[7:0]
THR
W
N/A
This register holds the data bits to be transmitted. Bit 0 is the LSB and is
transmitted first. The MSB may be transmitted first, if it is configured with the
E_MSB_TX bit in the MM1. The reset value is unknown since the register is
loaded with data in the transmit FIFO. The DLAB, bit 7 of LCR, must be 0 to
write to this register. This register is write only. Reading from this register with
the DLAB 0 reads the
register value.
Table 470 •
FCR
Bit
Number
Name
R/W
Default
State
Description
[7:6]
RX_TRIG
W
0b11
These bits are used to set the trigger level for the Rx FIFO
interrupt. Rx FIFO trigger level (bytes) are:
0b00: 1 byte
0b01: 4 bytes
0b10: 8 bytes
0b11: 14 bytes
[5:4]
Reserved
W
0
Software should not rely on the value of a reserved bit. To
provide compatibility with future products, the value of a
reserved bit should be preserved across a read-modify-write
operation.
3
ENABLE_TXRDY_RXRDY W
0
Software must always set this bit to 1 for efficient data
transfer from transmit FIFO to PDMA.
2
CLEAR_TX_FIFO
W
0
Clears all bytes in the Tx FIFO and resets its counter logic.
The shift register is not cleared.
0: Disabled (default)
1: Enabled
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