Tandy 1000
Theory of Operation for RS-232
Technical Reference Manual
The
RS-232
asynchronous communications board has various modes of opera-
tion that can be selected by programming the WD8250 ACE. The WD8250
is
programmed by selecting the I/O address (3F8 to 3FE primary, and 2FB
to 2FE secondary), and writing data out to the board. Address bits
AO,
A
1,
and A2 are used to define the modes of operation by selecting the different
registers.
The
selection of certain registers
is
done by using the divisor latch
access bit (Bit
7)
of the line control register.
One interrupt
is
provided to the system for IRQ4 for primary operation, and
IRQ3 for secondary operation. This interrupt
is
active high. Bit 3 of the modem
control register must be
set
high
in
order
to
send interrupts
to
the system. When
this bit
is
high, any interrupts allowed by the interrupt enable register
will
cause
an interrupt.
Refer to Figure 16 for the Functional
Pin
Definitions, and Figures 17 and 18
for Timing Diagrams of the WD8250.
Figure 19 shows the Block Diagram for the RS-232 Adapter.
Figure 20 shows the Functional
Pin
Definitions for the 82S153 IFL.
78
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