TOPS-20 Commands Reference Manual

DEPOSIT

Modifies the contents of a specific memory location.

Format

@DEPOSIT (MEMORY LOCATION) address (CONTENTS) data

where:

address	is an octal number or a symbol.
data	is a symbolic or numerical expression.

Output

Status of Pages

When you complete a DEPOSIT command, the system gives you a message indicating the status of the page you are trying to change: "[New]" for previously nonexistent pages, "[Shared]" for those having Copy-on-Write status, or "?Can't write that page" for other pages. (See also Hints - Setting the Page-access of Memory Pages, below.) However, no message is printed for deposits made to private pages.

Hints

Using Symbols

For symbols that are defined in multiple modules of a program, you can be specific by giving the module name followed by an ampersand (&) and the symbol name.

Using DDT Instead

Usually the DEPOSIT command is unnecessary, as the DDT program provides more powerful methods for modifying the contents of memory.

Abbreviating DEPOSIT Arguments

The contents of each memory location are represented as two 6-digit octal numbers. By inserting a pair of commas between these two numbers, you can abbreviate them. For example, to deposit 000004000050 into memory location 151003, use the command

@DEPOSIT 151003 4,,50

This is the same as

@DEPOSIT 151003 4000050

Note that you can also insert commas between expressions. For example, the command

@DEPOSIT 1 1+3,, 5+7

deposits 000004000014 into memory location 1. (Expressions are considered to be octal unless they contain an 8 or a 9, in which case they are considered to be decimal and are translated to octal.)

The DEPOSIT command itself can be abbreviated by the single letter D.

Deposit Address Defaults to the One Examined, and Vice Versa

The first argument of a DEPOSIT command defaults to the address examined by your most recent EXAMINE command. (You must press the ESCAPE key to take this default.) The argument of an EXAMINE command defaults to the address whose contents were modified by your most recent DEPOSIT command. Therefore you can examine a memory location, deposit a new value in it, and verify your action, while specifying the location only once. If you give DEPOSIT commands without intervening EXAMINE commands (or vice versa), the default address increases by 1 for each subsequent command.

Setting the Page-access of Memory Pages

If the system responds to a DEPOSIT command with an error message of the form, "?Can't write that page", give the SET PAGE-ACCESS COPY-ON-WRITE command for the page. Then give DEPOSIT again. If the system allows it, you will be given your own copy of the page to modify.

Using DEPOSIT With Inferior Processes

To modify memory for a process inferior to the one immediately below the TOPS-20 command processor, you must give the FORK command to specify this process before using DEPOSIT. Remember that for an inferior process to run, all superior processes must be running too. INFORMATION PROGRAM-STATUS tells you which processes these are.

Effect on Memory

The DEPOSIT command changes one location in memory.

Related Commands

DDT	for calling a debugging program, allowing more efficient modification of memory
EXAMINE	for displaying the contents of a specific memory location
FORK	for selecting the process whose memory you want to modify
INFORMATION MEMORY-USAGE	for displaying a list of memory pages, their contents and status
SET PAGE-ACCESS	for making it possible to write to specified pages

Examples

Deposit a value in a memory location.
```
@DEPOSIT 1500 21
```
Modify a memory location, using symbols. Then examine the location.
```
@DEPOSIT T3+1 P+2 
@EXAMINE T3+1
T3+1/ P+2   (4/ 21)
```

Try to deposit a number into a page of memory that does not allow it. Examine memory, set the page to Copy-on-Write status, and try again (succeeding this time).

@DEPOSIT 716505 0
?Can't write that page
@INFORMATION MEMORY-USAGE

 216. pages, Entry vector loc 462207 len 254000

  Section 0          R, W, E, Private
0-11          Private   R, W, E
20            Private   R, W, E
400-401       Private   R, W, E
402-660       <FIELD-IMAGE>FORTRA.EXE.3   13-271   R, CW, E
700-730       <NEXT-RELEASE>PA1050.EXE.4   1-31   R, E
731-733       Private   R, W, E

@SET PAGE-ACCESS 716 COPY-ON-WRITE
@DEPOSIT 716505 0
 [Shared]
@EXAMINE 716505
716505/  0

Check your program status (the arrow [=>] indicates your current process [fork]). Select an inferior process, deposit a value into a memory location, and verify that memory for the superior process is not changed to this.

@INFORMATION PROGRAM-STATUS
 Used 0:00:05 in 0:10:11
 TOPS-20: 0:00:03.5
 SET UUO-SIMULATION (FOR PROGRAM)
 SET CONTROL-C-CAPABILITY (OF PROGRAM)
 => MACRO (1): ^C from IO wait at 775701, 0:00:00.3
      Fork 2: HALT at 472052, 0:00:00.1
@FORK 2
@DEPOSIT 3500 12
@EXAMINE 3500
3500/   12
@FORK 1
@EXAMINE 3500
3500/   202200,,1136

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