Printing Barcodes with MAI OpenBasic

Printing Barcodes with MAI OpenBasic
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MAI OpenBasic systems often used a line printer equipped with a special internal module to print barcodes. These printers are no longer available, and as they succumb to old age they must be replaced with currently-available printers which do not support the same barcode command syntax. Barcodes can be printed on laser printers with a little modification of the OpenBasic application software.

The first solution involves adding a BarDIMM module to a Hewlett-Packard LaserJet printer. Product and programming details can be found at http://www.makebarcode.com/reviews/addin/barsimm.html. This solution is effective and relatively easy to implement; all of the complicated calculations and formatting are done in the BarDIMM, so the OpenBasic code changes are relatively simple. The downsides are that the BarDIMM works only with Hewlett-Packard printers and that one module must be purchased for each printer; this is not too bad for one printer, but can get expensive if several printers are involved.

The second solution involves downloading a PCL barcode font to a laser printer; the particular brand of printer does not matter, as long as it is compatible with the PCL-5 printer command language (most laser printers are). Here is a link to information (including downloadable manual and demonstration versions) for several PCL font kits and, for heavy-duty users, a font generator program: http://www.makebarcode.com/software/printerfonts.html. The downloadable manuals go into a fair amount of detail on using the PCL fonts. The remainder of this article will deal with using Code 39 and Code 128 with OpenBasic.

Code 39

Code 39 (info at http://www.makebarcode.com/specs/code_39.html) is an excellent general-purpose barcode that can contain letters and numbers and is very easy to use. To download a font, simply copy it to the printer's port; it is best to do this just before running a print job that will require barcodes. To modify the OpenBasic code which generates the report, first remove the barcode instructions for the old printer; there will typically be a command to start the barcode followed by the data, then finished with a command to stop the barcode. Add new code to select the correct PCL barcode font, print the data, and then switch back to a regular text font.

The following example assumes that the printer is attached to Port 6 and that the data we wish to print is in OUTS$. The string BARON$ is set to an escape sequence that selects font number 25501 (each font in a PCL font kit has a different ID number, so any font can be downloaded and selected by number; use the ID number which is embedded in the particular font you wish to use). The string BAROFF$ is loaded with an escape sequence that switches back to the printer's default font (typically Courier). Asterisks are added before and after the data to represent the start/stop characters required by the barcode scanner.

Note: It is important to send the final string to the printer in a single instruction to prevent the system from inserting any extra characters while the barcode font is still active. With some types of barcodes a control code (carriage return, for example) can be printed as a barcode character.

10000    LET BARON$=CHR(27)+"(25501X"
10002    LET BAROFF$=CHR(27)+"(3@"
10004    LET OUTS$=BARON$+"*"+OUTS$+"*"+BAROFF$
10006    PRINT (6)OUTS$
10008    RETURN

Code 128

Code 128 (info at http://www.makebarcode.com/specs/code_128.html) includes upper and lower case alpha characters, numbers, all the standard ASCII symbols, and all of the standard ASCII control code. Formatting a Code 128 barcode is more complex because, unlike Code 39, it requires calculation of a checksum. In the example below the barcode will be printed using Code 128 "Subset B'; this is the most commonly-used subset which includes all of the standard printable ASCII characters. Subset A includes the control codes, and Subset C provides a means for compressing all-numeric data into a more compact barcode. Details on the different subsets can be found in the manuals for the PCL Barcode Font Kits and Font Generator referenced above. We will stay with Subset B in this example for simplicity.

The lowest ASCII value for a printable character is 32 (space); in the Code 128 character set, this is character 0. When calculating the checksum, the Code 128 values are used; to convert to a printable ASCII character we have to add 32. The Code 128 value of the Start Subset B character is 104 (printed as ASCII 136), and the value of the Stop character is 106 (printed as ASCII 138). More excruciating detail is available in the PCL Font manuals, http://www.makebarcode.com/software/printerfonts.html.

At line 10026 in the example we are formatting a Transparent Print command. This instruction tells the printer that the next X number of characters are to be printed, and not interpreted as command characters. This is very important with Code 128 since it is perfectly possible for a checksum to work out to the same value as the Escape code. The Transparent Print command prevents the printer from accidentally interpreting a checksum as a command character.

:
:
00100    REM PRINT "HELLO" AS A BARCODE
00102    LET OUTS$="HELLO"
00104    GOSUB 10000
00106    REM CONTINUE WITH REST OF APPLICATION
:
:
10000    REM *** SET UP ESCAPE SEQUENCES TO TURN BARCODE ON AND OFF
10002    LET BARON$=CHR(27)+"(25501X"
10004    LET BAROFF$=CHR(27)+"(3@"
10006    REM *** CALCULATE CHECKSUM BEGINNING WITH START CHAR
10008    LET CHECK=104
10010    LET MULTI=1
10012    FOR XYZ = 1 TO LEN(OUTS$)
10014    LET CHECK=CHECK+((ASC(OUTS$(XYZ,1))-32)*MULTI)
10016    LET MULTI=MULTI+1
10018    NEXT XYZ
10020    REM *** DO MODULO 103 DIVISION TO GET FINAL CHECKSUM
10022    LET CHECK=MOD(CHECK,103)
10024    REM *** FORMAT TRANSPARENT PRINT ESCAPE SEQUENCE
10026    LET TRAN$=CHR(27)+"&p"+STR$(LEN(OUT$)+3)+"X"
10028    REM *** BUILD THE FINAL STRING
10030    LET OUTS$=BARON$+TRAN$+CHAR(136)+OUTS$+CHAR(CHECK+32)+CHAR(138)+BAROFF$
10032    REM *** SEND IT TO THE PRINTER
10034    PRINT (6)OUTS$
10036    RETURN

The result should be a perfect Code 128 barcode. Other AppNotes on Code 128 checksum calculations can be found at http://www.makebarcode.com/info/appnote/app_001.html and http://www.makebarcode.com/info/appnote/app_004.html.