Siemens SINUMERIK 828D Programming Manual page 48

Creating an NC program
3.2 Available characters
NOTICE
Take care to differentiate between the letter "O" and the digit "0".
Note
No distinction is made between upper and lower-case characters (exception: tool call).
Note
Non-printable special characters are treated like blanks.
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Programming Manual, 07/2010, 6FC5398-1BP40-0BA0
Fundamentals