Program Segment Prefix: Difference between revisions

Revision as of 14:22, 12 July 2007

Revision as of 20:13, 12 July 2007

Line 2:

It has the following structure:

<table{| border="1">

| Offset

<tr><td>Offset</td><td>Size</td><td>Contents</td></tr>

| Size

<tr><td>00-01</td><td>Code</td><td>CP/M exit (always contain INT 20)</td></tr>

| Contents

<tr><td>02-03</td><td>Word</td><td>Memory size in paragraphs</td></tr>

|-

<tr><td>04</td><td> </td><td>Reserved</td></tr>

| 00-01

<tr><td>05-09</td><td>Code</td><td>Far call to CP/M compatibility code within DOS</td></tr>

| Code

<tr><td>0A-0D</td><td>[[DWord]]</td><td>Terminate address of previous program (old INT 22)</td></tr>

| CP/M exit (always contain INT 20)

<tr><td>0E-11</td><td>DWord</td><td>Break address of previous program (old INT 23)</td></tr>

|-

<tr><td>12-15</td><td>DWord</td><td>Critical error address of previous program (old INT 24)</td></tr>

| 02-03

<tr><td>16-17</td><td>Word</td><td>Parent psp segment (PSP of caller - usually command.com - internal)</td></tr>

| Word

<tr><td>18-2B</td><td>Bytes</td><td>[[Job File Table]](JFT) (internal)</td></tr>

| Memory size in paragraphs

<tr><td>2C-2D</td><td>Word</td><td>Environment segment</td></tr>

|-

<tr><td>2E-31</td><td>DWord</td><td>SS:SP on entry to last INT 21 call (Internal)</td></tr>

| 04

<tr><td>32-33</td><td>Word</td><td>Max open files (Internal - see below)</td></tr>

|

<tr><td>34-37</td><td>DWord</td><td>Handle-entries address (Internal - see below)</td></tr>

| Reserved

<tr><td>38-4F</td><td> </td><td>Reserved</td></tr>

|-

<tr><td>50-52</td><td>Code</td><td>Far call to DOS (always contain INT 21 + RETF)</td></tr>

| 05-09

<tr><td>53-5B</td><td> </td><td>Reserved</td></tr>

| Code

<tr><td>5C-6B</td><td> </td><td>Unopened Standard FCB 1</td></tr>

| Far call to CP/M compatibility code within DOS

<tr><td>6C-7F</td><td> </td><td>Unopened Standard FCB 2 (overwritten if FCB 1 is opened)</td></tr>

|-

<tr><td>80</td><td>Byte</td><td>Number of characters on command-line</td></tr>

| 0A-0D

<tr><td>81-FF</td><td>Bytes</td><td>Command-line (terminated by a 0Dh)</td></tr>

| [[DWord]]

</table>

| Terminate address of previous program (old INT 22)

|-

| 0E-11

| DWord

| Break address of previous program (old INT 23)

|-

| 12-15

| DWord

| Critical error address of previous program (old INT 24)

|-

| 16-17

| Word

| Parent psp segment (PSP of caller - usually command.com - internal)

|-

| 18-2B

| Bytes

| [[Job File Table]](JFT) (internal)

|-

| 2C-2D

| Word

| Environment segment

|-

| 2E-31

| DWord

| SS:SP on entry to last INT 21 call (Internal)

|-

| 32-33

| Word

| Max open files (Internal - see below)

|-

| 34-37

| DWord

| Handle-entries address (Internal - see below)

|-

| 38-4F

|

| Reserved

|-

| 50-52

| Code

| Far call to DOS (always contain INT 21 + RETF)

|-

| 53-5B

|

| Reserved

|-

| 5C-6B

|

| Unopened Standard FCB 1

|-

| 6C-7F

|

| Unopened Standard FCB 2 (overwritten if FCB 1 is opened)

|-

| 80

| Byte

| Number of characters on command-line

|-

| 81-FF

| Bytes

| Command-line (terminated by a 0Dh)

|}

The PSP is most often used to get the command line arguments of a DOS program, for example the command "foo.exe -a -f" executes foo.exe with the arguments '-a' and '-f'.