(see Configuration section) define the base
addresses of the serial ports. The Serial Port
registers are located at sequentially increasing
addresses above these base addresses. The chip
contains two serial ports, each of which contain a
register set as described below.
TABLE 33 - ADDRESSING THE SERIAL PORT
DLAB*
A2
0
0
0
0
0
0
1
1
1
1
0
0
A1
0
0
0
1
1
1
0
0
1
1
0
0
A0
0
0
1
0
0
1
0
1
0
1
0
1
REGISTER NAME
0
0
Receive Buffer (read)
Transmit Buffer (write)
0
Interrupt Enable (read/write)
Interrupt Identification (read)
FIFO Control (write)
X
X
X
X
X
X
X
1
Line Control (read/write)
Modem Control (read/write)
Line Status (read/write)
Modem Status (read/write)
Scratchpad (read/write)
Divisor LSB (read/write)
Divisor MSB (read/write
1
*Note: DLAB is Bit 7 of the Line Control Register
72
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