Baud Rate - AXIOMTEK AX10445 Series User Manual

AX10445 Module Series User's Manual
Figure 3 Sample of Asynchronous Transmission Format
The serial port hardware on MS-DOS systems is based on
the UART (Universal Asynchronous Receiver Transmitter),
and is programmable through a set of 8-bit registers. These
registers are accessible to the programmer via base port
addresses. These port addresses are assigned sequentially.
In the IBM PC, the two serial ports COM1 and COM2 are
assigned with base port addresses 3F8h and 2F8h
respectively. For more information, please refer to the data
book.
There are seve n physical registers in the UART (which plays
an important role in the AX10445 Series), as illustrated in
Figure 4. A brief information of each register will be given
below.
NOTE:
F o r n o r m a l U A R T o p e r a t i o n , t h e D L A B ( t h e m o s t
significant bit of base address +3) must always be
set to 0. Set DLAB = 1 only when configuring the

baud rate.

Base Address 0
Base Address +1
Base Address +2 (IIR)
IIR (2)
1
1
0
0
14
: used to store a single character that is being
received or transmitted.
: used to enable or disable interrupts that the
serial port is capable of generating.
: reports the identity of an interrupt.
IIR (1) IIR (0)
1 0
0 0
1 0
0 0
Interrupt ID
Line status
Received data
Transmit buffer empty
Modem status
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