SPROGS Paper No 5:

P M Nelson

January 19 1971

Purpose

To provide a quick reference summary of the instruction set of the PDP 15.

1. INTRODUCTION

The following program will produce listings of PDP15 files on the Atlas lineprinter rather than the PDP15 teletype. The program is quite fast and we have permission to put it in the Atlas EXPRESS queue even when the lineprinter output expected exceeds 1000 lines.

2. INITIALISATION OF MAGNETIC TAPE

The information to be listed on Atlas must be directed to a 7-track magnetic tape on the PDP15 which has been initialised with a directory so that the magnetic tape can behave like any other file-orientated device. The tape must be written in 556 bpi, odd parity. This is set as the standard output from MTA, so that as far as the basic software is concerned this need not worry the user. He will get this unless he defines it otherwise.

The directory on the magnetic tape is initialised by MTDUMP as follows:

A MTAO    1
A DTAO   -4
A TTAO    3
GLOAD 
(      )
+MTDUMP <ALT MODE> 
(     _) 
F  1, 05 
NEWDIR 1 

The monitor assignments ensure that loading is from the monitor tape where MTDUMP is kept and assigns a positive DAT slot 1 to MTA for MTDUMP to use. The FORMAT statement (F) sets tape 1 to ODD parity and 556 bpi. Note that a letter Oh and not a zero is required. The tape unit should of course have a tape counted on-line at the load point and the unit number set to 1. A unit other than 1 could have been used in the above example.

3. OUPUT FROM THE PDP15

Once the magnetic tape has been initialised, output can be sent to it using the PIP or any of the standard compilers. To list a file stored on DEC tape it would be reasonable to use a PIP command such as

T MT1 FILENM +- DT1 FILENM (A) 

The listing generated by MACRO or F4 can be directed to the magnetic tape by assigning:-

   A MTA1 -12 

before entering the compiler. The program listing generated by the compiler will then be output to the magnetic tape. Diagnostic information will still appear on the teletype.

4. ACTIVE AND INACTIVE FILES

It is not possible to selectively overwrite parts of a magnetic tape. If a new copy of an existing file is sent to a magnetic tape, it is added at the end of the and the directory updated to point to this new area. The old copy is still on the magnetic tape but has no pointer to it from the directory. It is called an inactive file. Files which have directory entries pointing to them are called active files. (It is possible to remove inactive files from a magnetic tape using the CULL directive in MDUMP).

5. JOB DESCRIPTION

Assuming a magnetic tape has been generated on the PDP15 it can be listed on Atlas with the following program:-

J0B I0042 EXPRESS NELSON LIST 
STORE 8 BLOCKS 
COMPUTING 10 SECONDS 
TAPE IBM 2 NELSON PDP15 FILES 
OUTPUT 0 LINEPRINTER 1000 LINES 
DISC 1 R121 LMAGTAP 
COMPILER SPECIAL 
*END-COMPILING 
LIST 
( data) T
7 
8 

The user should put his own name and number. The IBM tape must be 2 but the title 'NELSON PDP15 FILES' should be defined by the user. If he requires the tape back then some message is usually necessary. The computing and output statements may, of course, be changed by the user.

Approximately 1000 1ines of output is generated every 6 seconds.

6. DATA

The information on the IBM tape to be listed can be defined in the following ways:-

(1) ALL ACTIVE FILES

A single data card witch ALLUFILES in columns 72-80 is required.

(2) ALL FILES

A single blank data card.

(3) PARTICULAR ACTIVE FILES

The file name + extension must be put in columns 72-80 with one card per file.

The amount of output generated by the blank data card can be reduced by preceding it with a card defining a particular active file. The blank card will then print only the files on the tape past this point.

Thus the data:-

    XYZuuuBRC 
    uuuuuuuu 

will list the file XYZ followed by all files further down the tape than XYZ.

Note:- u = a space