Radio Shack 26-1145 - Page 13

Theory
of
Operation
The Radio Shack RS-232
Interface
is a versatile
programmable
interface which
will permit you to interface
with
almost
any
equipment which
is
RS-232-C
compatible.
There are
essentially two
different categories
of RS-232-C
equipment,
namely
data
terminal
equipment and
data-comm
(data communications)
equipment.
The Radio Shack RS-232-C
Interface
is configured
from the data
terminal's
point of
view,
for interfacing
with
data-comm equipment.
You can
control the
configuration
of the Interface
two
ways,
by
sense switch selection
or by direct selection
using
software
control.
Universal
Asynchronous Receiver-Transmitter
Figure
4
is a block diagram of
the RS-232-C
Interface.
The
heart of.
the Interface
is the UART (Universal
Asynchronous
Receiver-
Transmitter). This
MOS LSI device
(TR1602A)
contains
most
of the
hardware needed
to receive
and transmit
serial data. The UART
is an
industry standard, general
purpose,
programmable
device for
interfacing
an asynchronous serial
data channel
to the parallel data
structure of
a microprocessor.
The transmitter
section of the
UART converts
parallel data from
the microprocessor
into a
serial word which
contains the
data along with
start, parity and
stop
bits. The
receiver
section converts
a serial word
(with start,
data, parity and
stop bits) into parallel
data,
and verifies
proper data
transmission
by checking
parity and receipt
of a valid stop bit.
The
operation
of
the
UART
can
be programmed
as follows:
The
word
length
can
be
5, 6,
7 or 8 bits;
parity generation
and
checking
can be inhibited,
the
parity may
be
even
or odd and
the number of stop bits may
be either
one
or two, with
one-and-one-half when transmitting
a 5-bit code.
The UART
contains several
internal
registers
which will
permit
you
to configure
the
serial data channel,
monitor
the UART
status, load
data to be transmitted,
and read
data that is
received on the serial
data
channel.
Later
we will discuss the
UART
registers
in more
detail.
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