Fastcom 232/8-ISA, Справочник по аппаратуре, Страница: 15 / 26

9
SWITCH DESCRIPTIONS
There are three dip switches on the FASTCOM: 232/8-ISA, labeled SW1, SW2, and SW3 (See Board Layout
Illustration for location). Switch 1 (labeled Base Address) is used to set the I/O address of the FASTCOM: 232/8-
ISA board. Switch 3 (labeled IRQ) serves two functions: it selects the IRQ level for the board and is used to
enable/disable interrupt sharing. Switch 2 is used to select upper IRQ levels.
SWITCH 1, ADDRESS
Switch 1 decodes the PC address lines as follows:
Address lines A6 through A13 are decoded by the setting of SW1
and set the base address of the FASTCOM: 232/8-ISA. Address
lines A3, A4, and A5 are used on the board to select which port (1
to 8) you want to use. Address lines A0, A1, and A2 are used to
select the registers within the UARTS.
ON
1 2 3 4 5 6 7 8
Address Line Hex value
A12 1000
A11
A10
A9
A8
A7
A6
800
400
200
100
80
40
A13 2000
The above diagram illustrates a base address of 280 Hex (factory
default). Note that when a switch is ON it represents a "0" in the
corresponding bit position (not a "1" as you might expect). Also, a
switch that is OFF represents a "1" in the corresponding bit
position. (If you would like to know why this is reversed, read a
technical data sheet for the address decoder chip, a 74LS682).
So, the SW1 diagram can be decoded as follows:
A13 A12 A11 A10 A9 A8 A7 A6
0 0 0 0 1 0 1 0
You can determine the I/O address of the board by adding the Hex values for each address line that is set to a
"1". In the illustration, only address lines A7 and A9 are set to "1". So, add the Hex value of A9 (200H) and A7
(80H), and the result is the I/O base address (200H + 80H = 280H).
Switch 1 is referred to as the Base Address switch because it marks the beginning address of the first channel on
the FASTCOM: 232/8-ISA board. The other channels are addressed as an offset to the first channel. For
example, if we set the Base Address to 280H, note the address of each channel:
CHANNEL
BASE OFFSET ADDRESS
CHANNEL 1 = 280H + 0H 280H
CHANNEL 2 = 280H + 8H 288H
CHANNEL 3 = 280H + 10H 290H
CHANNEL 4 = 280H + 18H 298H
CHANNEL 5 = 280H + 20H 2A0H
CHANNEL 6 = 280H + 28H 2A8H
CHANNEL 7 = 280H + 30H 2B0H
CHANNEL 8 = 280H + 38H 2B8H
We have provided a comprehensive guide to setting the address switch in
Appendix A.