09.95 12 Functional Descriptions
12.10.2 Control of predecoding (SW 5 and higher)
12.10.2 Control of predecoding (SW 5 and higher)12.10.2.1 Corresponding data
• NC MD 5052* bit 6 Programmed predecoding with G171/G172
• Maximum number of predecoded blocks
• Real number of predecoded blocks
Function description
With the introduction of block buffer management and flexible memory configuration, the
number of predecoded blocks per channel (SW 4 and higher) has risen to over 3500 blocks
(8 MB CPU, 1 channel). However, the user should note certain general conditions:
• On program start, or after a "Clear buffer" (@714), the predecoding function fills the
available block buffer and only leaves a little CPU time for the display, which is then slow.
• The refresh (program stop/start, single block) takes a long time because it is performed on
all predecoded blocks.
• The number of predecoded blocks can be limited with the channel-specific setting data
SD 204* When the program is run in a small value should be set here (2 to 10).
• The real number of predecoded blocks is displayed in NC SD 206*. See the description of
the setting data.
• The two setting data are displayed in the program control display.
Control by the user of predecoding (example):
The main application of the function is testing part programs. In this case the setting data 204*
must be set to 2 to limit predecoding and to accelerate testing (e.g. in single block mode).
It is also possible to control predecoding during operation: An auxiliary function (H1234=1234)
can be programmed in the part program so that the PLC sets a read-in disable and then scans
the setting data 204* for the number blocks. Once these blocks have been predecoded
(displayed in SD 206*), the read-in disable is cancelled again. The predecoded blocks are now
processed without any drop in velocity.
© Siemens AG 1992 All Rights Reserved 6FC5197- AA50 12–73
SINUMERIK 840C (IA)