two, and one, hence the maximum value of 8+4+2+1 = 15.
A serial port's address is a 16-bit quantity that is most often expressed
in four hexadecimal (base 16) digits. A hex digit can hold a value from 0 to
15 (decimal), and is made up of four binary bits given weights of eight, four,
A possible serial port address is 5220 hex. The example below shows
how the hex digits are broken down into binary bits.
Bit weight
Binary bits
Sum of bits
Hex digits 220
5
8 4 2 1 8 4 2 1 8 4 2 1 8 4 2 1
0+4+0+1 0+0+2+0 0+0+2+0 0+0+0+0
0 1 0 1 0 0 1 0 0 0 1 0 0 0 0 0
0 1 0 1 0 0 1 0 0 0 1 0 0 0 0 0
These address bits are set by the switches.
All other bits are considered to be zero.
Figure 5 --- Examination of a serial port base address
Switch on
bit = 0
Switch off
bit = 1
Factory default setting --- 0300 hex
ON
0200
0
1
123456

SW2

0000
0
0
3
123456

SW1

0
Position 6 of SW2 is used to enable or
disable the interrupt status register.
0
(no digits)
Another Example --- 54A0 hex
ON
20 0 8 0
A
123456

SW2

0001
5
4
4
123456

SW1

4
0
(no digits)
A4 - A0 are zero for the base address.
ON
ON
Figure 5 --- Serial Port base I/O address selection switchesQS-100D User's Manual 2-3