LSI Logic Confidential
15-80
Serial I/O Port
Copyright © 2001, 2002 by LSI Logic Corporation. All rights reserved.
15.5.6 SIO UART1/UART2 Registers
UART1 Receive Buffer / Transmit Holding / Divisor Latch LSB Register
(UART1_RBR0_THR0_DLL1)
UART2 Receive Buffer / Transmit Holding / Divisor Latch LSB Register
(UART2_RBR0_THR0_DLL1)
In effect, three registers share the offset address 0x100: UART1_DLL,
UART1_THR, and UART1_RBR.
Similarly, three registers share the offset address 0x180: UART2_DLL,
UART2_THR, and UART2_RBR.
The value of the DLAB bit in the UART* Line Control register determines
which register is physically written or read, as shown below:
•
Write UART*_DLL when DLAB = 1
•
Write UART*_THR when DLAB = 0)
•
Read UART*_RBR when DLAB = 0
In any case, each of these three registers is always accessed via the
same software name: UART1_RBR0_THR0_DLL1 or
UART2_RBR0_THR0_DLL1.
UART1 / UART2 Divisor Latch LSB Register (DLL)
Offset = 0xBE0100 / 0xBE0180
Write only
Default = 0x0000 0000
DLSB
Divisor LSB
31:24
The baud rate generator implements two 8-bit divisor
latches that can be write only accessed by the external
host processor or SPARC processor. The processor can
load 16-bit data into DLM and DLL (DLM holds the eight
most significant bits, DMSB, and DLL holds the eight
least significant bits, DLSB) to obtain an output (nBD-
31
24
23
16
DLSB
RSVD
15
0
RSVD