Review the hex dump for missing codes or codes that have been changed or added to. Typical things to look for include: an <LF> (ASCII 0AH) added after the <CR> (ASCII 0DH) code, <HT> (ASCII 09H) changed into a series of spaces (ASCII 20H), or <FF> (ASCII 0CH) changed into a series of <LF> (ASCII 0AH) codes.

The program illustrated above could, of course, be written in any language that you wish to investigate.

Beyond finding problem codes, the hex dump feature also provides a way to check which codes are actually being sent to the printer by a program. Just turn on the hex dump feature and run the program. Then interpret the codes that are printed out.

If you are investigating a program that uses the graphics op- tions, be prepared for a lot of printing since each byte of graphics data is printed in hex. This can be several pages of hex dump numbers. You can usually stop the printer after a couple of print lines of graphic data have been printed.

Figure 7-2 shows the hex dump printout of the first graphics demonstration program in Chapter 6. If you study the codes you can see the graphics option command and the graphics data, followed by a <CR> <LF>

1B

2A

0 0

0E

0 0

0 3

0 7

1F

3F

7E

7C

7 0

6 0

5C

42

21

19

05

0 3

0D

0A

 

 

 

 

 

 

 

 

 

Figure 7-2.Hex dump printout of Chapter 6 graphics program

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