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3.2 UART Registers
3.2.1 Receive buffer/transmit hold register
This register (RBR/THR: 5000_0000H (UART0), 5001_0000H (UART1), 5002_0000H (UART2)) is used to read
received data and write data to transmit.
This register functions as the receive buffer register (RBR) when read, or as the transmit hold register (THR) when
written. In FIFO mode (bit 0 of FCR register = 1), the FIFO buffers are accessed.
15
14
0/D7
0/D6
7
6
D7
D6
Name
R/W
0/D[7:0]
R
W
D[7:0]
R
W
Operation in non-FIFO mode (bit 0 of FCR register = 0)
Received data is read out by reading this register, and data written to this register is stored as data to transmit.
Data of the lowest bit (D0) is transmitted or received first.
Only the lower bytes (D[7:0]) are used. This register can be accessed in byte units via the host bus interface. If
this register is accessed in 2-byte units in non-FIFO mode, the higher bytes (0/D[7:0]) become invalid (all zeros
returned when read, ignored when written) and only the lower bytes are used.
Operation in FIFO mode (bit 0 of FCR register = 1)
Received data is read out from the receive FIFO by reading this register, and data written to this register is
stored into the transmit FIFO as data to transmit. This register can be accessed in 1- or 2-byte units via the host
bus interface. Data of the lowest bit (D0) is transmitted or received first.
If this register is read in byte units, all zeros are returned from the higher bytes (0/D[7:0]) and data in the lower
bytes (D[7:0]) becomes valid. If this register is written, the higher bytes become invalid and only the lower bytes
are used.
The FIFO capacity is selected by using bit 5 of the FCR register.
The 16-byte FIFO mode is selected (16550 mode) by setting bit 5 of the FCR register to 0, and the 64-byte
FIFO mode is selected by setting bit 5 of the FCR register to 1.
CHAPTER 3 REGISTERS
13
12
0/D5
0/D4
5
4
D5
D4
Bit
After Reset
15:8
Undefined
Reads received data in 2-byte units.
These bits are not used for 1-byte access. Zeroes are returned.
Writes data to transmit in 2-byte units.
These bits are not used for 1-byte access. Writing is ignored.
7:0
Undefined
Reads received data.
Stores data to transmit.
User's Manual S19262EJ3V0UM
11
10
0/D3
0/D2
3
2
D3
D2
Function
9
8
0/D1
0/D0
1
0
D1
D0
13
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