> Tracy Johnson wrote:
> 
> >I have difficulty understanding how a bar code can't be 
> scanned due to 
> >a data issue.  It can be perfectly good garbage, but you 
> should be able 
> >to "scan" the garbage.
> 
John Clogg answers:
> I believe barcodes contain checksums and/or parity to prevent reading 
> erroneous data.

On some models of bar code readers, the checksums/parity can be turned
off for testing purposes.  In cases when erroneous data of which you
speak are usually of the smudged ink or fuzzy variety, then you wouldn't
want the reader device to get fooled.

In other words, erroneous barcodes shouldn't be "printing" at all.  If
valid escape sequences are sent to print a barcode, you're still going
to get a barcode, even if the data is garbage.  Sometimes they end up as
NULL bar codes, with parity stripes on both sides of nothing, then the
reader will put in a carriage return for the user.  Then the reader
outputs a blank.

I wondered if the original question meant there were no bar codes at
all.  But I refrained since it only said they couldn't be scanned.
Which told me there was some form of barcode.

When the the HP256x printer changed from Serial to Network, was the
Barcode option also removed?  Was the printer interface also changed
from Serial to Parallel at the same time to attach to a print server
box?

I mean, does a valid barcode still appear on the printer Self-Test
report?

Or are the bar-codes generated at the host?  (I once saw some COBOL code
that "forced" barcoding on a 256x printer that did not have the barcode
option.  It printed dot by dot, not with typical HP-PCL barcode-escape
codes.)


Tracy Johnson
Measurement Specialties, Inc. 

BT







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