4. Addressing Ports
4.1 Setting the address
The base address of each port of the DS-200/300 is set using two DIP
switch packs. When setting the address selection switches, a switch in the
"ON" position specifies that the corresponding address line must be a
logic 0 for the port to be selected. Similarly, a switch in the "OFF"
position forces the corresponding address line to be a logic 1 for the port
to be selected.
A full sixteen bit address decode is implemented to reduce the chance of
address conflicts with other adapters in the system. Each serial port on
the DS-200/300 uses 8 consecutive I/O locations. The two ports reside in
their own independent block of I/O space in eight byte increments.
Switches SW1 and SW2 select address lines A15 through A3 for Serial 0
and switches SW3 and SW4 select address lines A15 through A3 for Serial
1. The remaining address lines (A2, A1 and A0) are used by the UART to
select the register being accessed. The sixth position on SW2 is used to
enable or disable Serial 0 and the sixth position on SW4 is used to enable
or disable Serial 1.
Figure 5 shows how the switches on the DS-200/300 represent the address
values for serial ports. This figure can be used to explain the examples
shown in Figure 6.
DS-200/300 User's Manual
4-1
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