Intel
®
81341 and 81342—UARTs
Intel
®
81341 and 81342 I/O Processors
Developer’s Manual
December 2007
888
Order Number: 315037-002US
15.4
Register Descriptions
There are 15 registers in each UART. The registers are all 32 bit registers, but only
lower 8 bits have valid data. The 12 UART registers share eight address locations in the
MMR address space. Table 561 shows the registers and their addresses as offsets of a
base address. The base address for each UART is 32 bits and is internal bus address
offset 2300H for UART 0, and 2340H for UART 1. Note that the state of the Divisor
Latch Bit (DLAB), which is 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.
Table 561. UART Register Addresses as Offsets of a Base
UART Register
Addresses
DLAB Bit Value
Name
Register Accessed
Base
0
UxRBR
UART x Receive BUFFER (read only)
Base
0
UxTHR
UART x Transmit BUFFER (write only)
Base + 04H
0
UxIER
UART x Interrupt Enable (R/W)
Base + 08H
X
UxIIR
UART x Interrupt I.D. (read only)
Base + 08H
X
UxFCR
UART x FIFO Control (write only)
Base + 0CH
X
UxLCR
UART x Line Control (R/W)
Base + 10H
X
UxMCR
UART x Modem Control (R/W)
Base + 14H
X
UxLSR
UART x Line Status (Read only)
Base + 18H
X
UxMSR
UART x Modem Status (Read only)
Base + 1CH
X
UxSPR
UART x Scratch Pad (R/W)
Base
1
UxDLL
UART x Divisor Latch (Low Byte, R/W)
Base + 04H
1
UxDLH
UART x Divisor Latch (High Byte, R/W)
Base + 24H
X
UxFOR
UART x FIFO Occupancy Register (R/W)
Base + 28H
X
UxABR
UART x Autobaud Control Register (R/W)
Base + 2CH
X
UxACR
UART x Autobaud Count Register (read only)
Table 562. UART Unit Registers
Section, Register Name, Acronym, page
Section 15.4.1, “UART x Receive Buffer Register” on page 890
Section 15.4.2, “UART x Transmit Holding Register” on page 890
Section 15.4.3, “UART x Interrupt Enable Register” on page 891
Section 15.4.4, “UART x Interrupt Identification Register” on page 892
Section 15.4.5, “UART x FIFO Control Register” on page 894
Section 15.4.6, “UART x Line Control Register” on page 896
Section 15.4.7, “UART x Modem Control Register” on page 898
Section 15.4.8, “UART x Line Status Register” on page 900
Section 15.4.9, “UART x Scratchpad Register” on page 904
Section 15.4.10, “Divisor Latch Registers” on page 905
Section 15.4.11, “UART x FIFO Occupancy Register” on page 906
Section 15.4.12, “UART x Auto-Baud Control Register” on page 907
Section 15.4.13, “UART x Auto-Baud Count Register” on page 908