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Intel
®
IXP42X product line and IXC1100 control plane processors—Universal Asynchronous
Receiver Transceiver (UART)
Intel
®
IXP42X Product Line of Network Processors and IXC1100 Control Plane Processor
DM September 2006
344 Order Number: 252480-006US
If characters less than 8 bits are received, the characters will need to be right-justified.
For example, if a 5-bit data character is received having a binary value of 00101. The
data read from the Receive Buffer Register will be a hexadecimal 0x05. (Notice that the
three most-significant bits of the byte are filled with zeros.)
The UART transmit data pin is logic 1 and the transmit FIFO and receive FIFO pointers
are initialized to the empty value after reset.
10.4 Register Descriptions
There are 13 registers to monitor and control the UART. The registers are all 32 bits in
size, but only the lower 8 bits have valid data. The 13 UART registers share nine
address locations in the
I/O address space.
Note that the state of the Divisor Latch Bit (DLAB) — the most-significant bit of the
Serial Line Control Register — affects the selection of certain of the UART registers. The
DLAB bit must be set high by the system software to access the Baud Rate Generator
Divisor Latches.
10.4.1 Receive Buffer Register
Table 134. High-Speed UART Registers Overview
Address DLAB R/W Name Description
0xC8000000 0 R RBR Receive Buffer Register
0W THRTransmit Holding Register
1 R/W DLL Divisor Latch Low Register
0x C8000004 0 R/W IER Interrupt Enable Register
1 R/W DLH Divisor Latch High Register
0x C8000008 0/1 R IIR Interrupt Identification Register
0/1 W FCR FIFO Control Register
0x C800000C 0/1 R/W LCR Line Control Register
0x C8000010 0/1 R/W MCR Modem Control Register
0x C8000014 0/1 R LSR Line Status Register
0x C8000018 0/1 R MSR Modem Status Register
0x C800001C 0/1 R/W SPR Scratch Pad Register
0x C8000020 0 R/W ISR Slow Infrared Select Register
Register Name: RBR
Hex Offset Address: 0xC800 0000 Reset Hex Value: 0x00000000
Register
Description:
Receive Buffer Register
Access: Read Only.
31 87 0
(Reserved) RBR