6.42  Operating  mode  “Transfer  blockwise” 
Very  long  programs  (e. g. for  moulds),  which  are  normally  compiled  on  an  external  computer,  can  be  read  into 
the  TNC  151/TNC  155  via  the  RS-232-C  (V.24)  data  interface  block-by-block,  and  executed  simultaneously. 
Computers  with  bulk  memories  or  the  HEIDENHAIN  Floppy  Disc  unit  FE  401  may  be  used.  A  multitasking 
system  is recommended,  so that  the  computer  can  perform  other  tasks  whilst  being  linked  to  one  or  more 
TNC  155-units. 
The  host  coimputer  generally  requires  a special  purpose  software  for  transmission  of  data  to  and  from  the 
TNC  151/TNC  155. 
6.421  “Transfer  blockwise”  using  the  HEIDENHAIN  Floppy  disc  unit  FE  401 
When  in  the  FE-mode,  the  RS-232-C  (V.24)-interface  is automatically  adapted  to  the  FE  401,  regardless  of 
the  machine  parameters  which  have  been  programmed.  Mode  selection  is initiated  by  the  MOD-function 
(MOD-key  and  ENT-key). 
6.422  Tralnsfer  blockwise  via  EXT-mode 
TNC  151/TNC  155  is connected  to  the  external  computer  via  the  RS-232-C  (V.24)  data  interface  in  the 
operating  mode  “EXT”.  Control  characters  for  computer  link-up  are  specified  by  machine  parameters. 
Data  transmission  can  be started  from  the  TNC  151/TNC  155.  After  starting,  the  control  transmits  a heading 
block  to  the  external  computer.  This  heading  block  contains  the  program  number  and  information  specifying 
whether  transmission  is to  be  from  the  computer  to  the  control  or  vice-versa.  Transmission  of  this  heading 
block  is followed  by  the  machining  program. 
Each  block,  which  has been  transferred,  is checked  by  a “block  check  character  BCC”.  This  is an  important 
check  procedure  of  the  “transfer  blockwise”  mode,  since  there  are  no  further  checks  of  the  machining  program 
possible  between  data  transmission  and  program  execution. 
If  a transmitted  program  block  has been  recognized  as error-free,  the  next  block  is called  up.  An  erroneous  block 
has to  be  re-transmitted. 
Transferred  blocks  are  read  into  a buffer  memory  in  the  TNC  151  /TNC  155,  and  can  be executed  from  this 
memory.  During  program  run,  the  executed  blocks  are  deleted  and  new  blocks  are  read  into  the  memory. 
Continous  contouring  operation,  without  interruptions  is therefore  possible. 
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