INTRODUCTION
I. INTRODUCTION
The DS-202 is a dual channel RS-422 asynchronous
serial communications adapter for systems implementing
an ISA compatible I/O bus. Data is communicated
through two shielded D-9 connectors which provide
greater shielding from environmental noise. The DS-302
is an RS-485 version of the adapter.
The serial interface is implemented with a pair of
16450 Asynchronous Communication Elements (ACEs). The
16450 is compatible with the 8250 ACE found in the
original IBM PC/XT models. The optional 16550 ACE
provides an additional FIFO mode of operation which
reduces CPU overhead at higher data rates.
The DS-202 / DS-302 allows independent addressing
of each channel through a pair of address decode
switches (SW1 and SW2). These switches allow each
channel to be addressed in the I/O address range 0000H
through 07FFH. Each channel is also capable of
selecting and / or sharing one of six possible
interrupt request lines (IRQ 2,3,4,5,6,7).
II. BOARD
DESCRIPTION
A component diagram of the DS-202 / DS-302 showing
the locations of the 16450 ACEs, configuration jumpers,
address selection switches, and output connectors is
shown in figure 1. The first communication channel is
controlled by the ACE labeled U7, switch SW1 for
addressing, jumpers J2 and J5 for interrupt request
selection, jumpers J7 and J8 for output signal control,
and is output through connector CN1. The second
channel is controlled by the ACE labeled U8, switch SW2
for addressing, jumpers J3 and J6 for interrupt request
selection, jumpers J8 and J10 for output signal
control, and is output through connector CN2.
III. 16450/16550
FUNCTIONAL DESCRIPTION
The 16450 is an improved specification version of
the 8250 Asynchronous Communications Element (ACE)
found in the original IBM PC and PC/XT systems and is
functionally equivalent to the 8250. This ACE performs
serial-to-parallel conversion on received data and
parallel-to-serial conversion on data output from the
CPU.
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