AXIOMTEK AX10445 Series, Руководство пользователя

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AX10445 Module Series User
’
s Manual
Technical Reference
14
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 :
For normal UART operation, the DLAB (the most
significant bit of base a3) must always be
set to 0. Set DLAB = 1 only when configuring the
baud rate.
Base Address 0 : used to store a single character that is being
received or transmitted.
Base A1 : used to enable or disable interrupts that the
serial port is capable of generating.
Base A2 (IIR) : reports the identity of an interrupt.
IIR (2) IIR (1) IIR (0) Interrupt ID
1 1 0 Line status
1 0 0
Received data
0 1 0 Transmit buffer empty
0 0 0 Modem status