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The I/O for the decoder ICs is full
duplex, 7 bit ASCII. Both serial
and parallel interfaces are
available. The serial interface can
be converted to an RS232C
interface or connected directly to
another microprocessor for data
processing. The parallel interface
can be connected to a tri-level
bus through a 74LS245 or
equivalent. Feedback to the
operator is accomplished by
signals for an LED and a beeper.
In addition, there are
programmable functions covering
items such as code selection and
beeper tone.
The ICs are CMOS, in either a 40
pin DIP package or a 44 pin
PLCC package. All ICs require a
dedicated external data memory,
2K or 8K x 8 bit static RAM (only
1K is needed) and address latch
chip (a 74LS373 or equivalent).
The crystal frequency is 12.000
MHz.
Performance Features
Bar Codes Supported
The decoder IC is capable of
reading popular bar code
symbologies: Code 39 (Standard
or Extended), Interleaved 2 of 5,
and UPC/EAN/JAN.
Code 39 is an alphanumeric code,
and Extended Code 39 encodes
the full 128 ASCII character set
by pairing Code 39 characters.
Both can be read bi-directionally
with message lengths of up to 32
characters. An optional checksum
character can be used with these
codes, and the ICs can be
configured to verify this
character prior to data
transmission. Note that enabling
Extended Code 39 will disable
Code 39 since they are mutually
exclusive.
Interleaved 2 of 5 code, a
compact numeric only bar code,
can also be read bi-directionally
with message lengths from 4 to
32 characters. To enhance data
accuracy, optional checksum
character verification and/or
message length checking can be
enabled.
The following versions of the
UPC, EAN and JAN bar codes can
be read bi-directionally: UPC-A,
UPC-E, EAN-8, EAN-13, JAN-8,
and JAN-13. All versions can be
enabled simultaneously or
decoding can be restricted to
only the UPC codes.
UPC, EAN, and JAN codes
printed with complementary two
digit or five digit supplemental
encodations can be read in two
different ways. If the codes are
enabled without the supplemental
encodations, then only the main
part of symbols printed with
supplemental encodations will be
read. If the reading of
supplemental encodations is
enabled, then only symbols with
these supplements will be read.
Whenever supplemental
encodations are enabled, the bar
code symbols must be read in the
direction that results in the
supplements being scanned last.
Scanner Input
The decoder ICs are designed to
accept data from hand held
digital scanners or slot readers
with the following logic state:
black = high, white = low.
Scanner input can be disabled by
software command. This allows
an application program to control
when an operator can enter data,
preventing inadvertent data entry.
It also allows the program to
verify each scan before enabling
subsequent scans.
Data Communications
The serial port supports a wide
range of baud rates, parities, stop
bits, and terminator characters,
as described in Summary of
Features and Configuration
Control table. Software control
of data transmission is
accomplished with an Xon/Xoff
(DC1/DC3) handshake.
The parallel port data has odd
parity. The default terminator
character is a CR, but it can be
changed by software commands.
An Xon/Xoff (DC1/DC3) software
handshake is available to control
data transmission.
Feedback Features
Both audio and visual feedbacks
are possible with the decoder ICs.
In both cases, the outputs from
the ICs must be buffered before
driving the actual feedback
mechanism. An LED or beeper
connected to the decoder ICs can
be controlled directly by the IC,
with signals generated by
successful decodes or can be
controlled by the host system.