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STEP 5 Programming Language
Block preheader
Maximum length
Available blocks
2 - 14
The programmer also generates a block preheader (DV, DXV, FV,
FXV) for block types DB, DX, FB and FX. These block preheaders
contain information about the data format (for DB and DX) or the
jump labels (for FB and FX). Only the PG can evaluate this
information. Consequently the block preheaders are not transferred to
the CPU memory. You cannot influence the contents of the block
header directly.
A STEP-5 block can occupy a maximum of 32 767 words in the
program memory of the CPU (1 word corresponds to 16 bits).
You can program the following block types:
OB
1 to 39
FB
0 to 255
FX
0 to 255
PB
0 to 255
SB
0 to 255
DB
2 to 255
DX
3 to 255
Data blocks DB 0, DB 1, DB 2, DX 0, DX 1 and DX 2 contain
parameters. These are reserved for specific functions and you cannot use
them as normal data blocks.
Data block DX 2 is reserved for the 2nd serial interface and you should
not use it.
total 512
total 508
CPU 948 Programming Guide
C79000-G8576-C848-04
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