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		    SPECIAL PURPOSE SUBROUTINES		    SPECIAL PURPOSE SUBROUTINES		    _______ _______ ___________

			  FOR FORTRAN IV			  FOR FORTRAN IV			  ___ _______ __


	This list contains a brief description of subroutines written to
extend the capabilities of D.E.C.'s FORTRAN IV for the PDP-8 and PDP-12.
Most of the subroutines will run on either PDP-8 or PDP-12 systems
with or without a hardward FPP.  A few are obviously unique to the
PDP-12 because they use devices such as the LINK-tape or LINK-scope.
	These routines were written by:

		Robert W. Phelps
		Dept. of Rad. Biol. & Biophysics
		University of Rochester Medical Center
		Rochester, NY  14642

They are available from the author and from DECUS.
(If requests are made to the author, please include a marked
DEC or LINK tape and return postage.)




MODE8MODE8_____

	An 8-mode subroutine may be called from FORTRAN IV by
the following statements:

	EXTERNAL <name>
	CALL MODE8 (<name>, <arg1>, <arg2>, ... )

A maximum of six arguments are allowed and arguments not used
may be omitted.  Thus the simplest call is:

	EXTERNAL <name>
	CALL MODE8 (<name>)

If arguments are passed, they are truncated to integer values between
0 and 4095.  The values of the arguments are passed in both directions
just as in any other FORTRAN subroutine, however, arrays may
NOT be passed.

	8-mode code must be assembled by RALF and must be completely
page relocatable.  The subroutine is effectively called by the
following code in MODE8:

	CDF <calling field>
	CIF <field of subroutine being called>
	JMS <name>
	JMP <return to FORTRAN>
	  <value of argument 1>
	  <value of argument 2>
	   .
	   .
	   .

A sample program is included in the source of MODE8.
SPECIAL PURPOSE SUBROUTINE DIRECTORY (continued)


RLINK -- (Entry into READB)RLINK_____

      Allows single LINK tape blocks to be read into a 256
element array.  The calling sequence is:

	DIMENSION <buffer>(256)
	CALL RLINK (<block>, <buffer>)

Integer values between 0 and 4095 are read from block <block>
from the LINK format LINK-tape on unit one (1), and
are returned as elements of the array <buffer>.  The patch described
in the USR writeup must be included in FRTS so RLINK can determine
the highest field of core for a data buffer.  Unpredictable results
may occure if more than one device with a non-resident handler is
used without using USR to open the files.
	(RLINK is an entry point in the READB subroutine and thus
does not exist as an individual program.)


IOTIOT___

      Allows 8-mode IOT's to be issued.  Calling sequence:

      CALL IOT (INST, AC)

INST is the 8-mode IOT instruction in decimal.    				      _______

AC is the value of the accumulator when the instruction is
issued.  If the IOT changes this value, the new value is
returned.  This feature may be used to read the switch register
if the instruction LAS is issued in place of an IOT.


USRUSR___

      This routine allows run-time declaration of files.  The
calling sequence is:

      CALL USR (UNIT, DFNAME, FUNCT, ERROR)

For more information, see the accompanying documentation.


PLOTIT and PREVUPLOTIT     PREVU______     _____

      Additions to the FORTRAN IV plotting capability.  These
routines are described in the accompaning documentation.
SPECIAL PURPOSE SUBROUTINE DIRECTORY (continued)


TVTV__

      Allows ASCII (formatted) information to be displayed on the
LINKscope in the background mode when executing FORTRAN programs.
The routine is designed for more rapid interaction with the user
than is possible using the teletype as an output device.  The
calling sequence is:

      EXTERNAL TV
      CALL MODE8 (TV, UNIT)

UNIT is a logical unit number (usually defined to be NULL:).  The
current contents of the OS/12 buffer associated with this device
is displayed on the scope in the background mode.  The FORTRAN
function BACKSPACE allows overwriting a line and REWIND erases
the screen.
      Input from the keyboard using the LINKscope to display the
typed line is possible using the TVIN handler.  To use TVIN, the
NULL handler must be used as the output device associated with
the TV display and the buffers for both NULL and TVIN must be in
the same field.  (This will be the case if USR was used to
open these files.)  All standard formatted read commands are
allowed, e.g.

      READ (7, 100) I
  100 FORMAT (I5)

where 7 is the unit number associated with TVIN.  A device error
is printed if NULL does not exist or if the buffer fields of NULL and
TVIN are different.  TVIN can only be used under FORTRAN IV.


READB & WRITEBREADB	WRITEB_____	______

      Allows reading/writing binary files in FORTRAN.	The
calling sequence is:

      DIMENSION BUFR(256)
      CALL READB (UNIT, BUFR)
	 or
      CALL WRITEB (UNIT, BUFR)

This reads/writes the next block of 256 12-bit binary words
from/to logical unit number UNIT into/from the 256 element array
BUFR.	The values read/written are between 0 and 4095.

      The program will not read or write past an end of file.	To
check for an end of file, code the following:

      EXTERNAL EOF
      LOGICAL EOF
      IF (EOF) GO TO 900
      .
      <continue source code>
      .
  900 <process end of file>
SPECIAL PURPOSE SUBROUTINE DIRECTORY (continued)


	To load new subroutines into the FORTRAN library, the
subroutine's source must be assembled with the RALF assembler
and the ".RL" file then added to the FORTRAN IV library
with the program LIBRA.  An example of how this is done is
included in the accompanying writeup on the subroutine USR.
For more information, see the OS/8 handbook chapter on FORTRAN IV.