China DOS Union

### Collection of DEBUG Practical Mini Programs
－－This post is a reprint


### 1. Repair of Non-Physically Damaged Track 0 Floppy Disks
Such damage does not have obvious scratches or mildew on the floppy disk surface. Generally, its data can be restored, and the floppy disk can be reused.
The processing method is as follows:
Ⅰ. Enter DEBUG
Ⅱ. Take a good disk with an undamaged boot sector, insert it into the floppy drive
-L 100 0 0 1
Ⅲ. Insert the damaged disk into the floppy drive
-W 100 0 0 1
-Q
Note: The capacities of the good disk and the bad disk must be the same


### 2. Reading Data from Physically Damaged Track 0 Floppy Disks
For a disk with track 0 damaged, generally, it should be discarded. But you may as well try the following methods:
Magnetization treatment: Use a strong magnet to repeatedly move near the surface of the bad disk, but be careful not to touch the disk medium to avoid scratching the surface, then try formatting again.
Floppy disk flipping: Carefully open the disk, separate the magnetic sheet from the metal chip, then stick them together according to the original method, and then reformat.
Diskfix: I believe everyone uses Diskfix more, and its disk repair function is very useful. It can repair most disk surface errors.


### 3. Handling of Hard Disk Boot Failure
Format a floppy disk on a normal machine with no other data
Enter DEBUG
-L 0 2 0 1
-W 0 0 0 1
-Q
After booting the faulty machine with the system disk
Enter DEBUG again
-L 0 0 0 1
-w 0 2 0 1
-Q


### 4. Solution to Incorrect Floppy Disk Reading
If the following prompt appears when using a floppy disk
General failure error reading drive A
The following method can be used to solve it:
Insert a good disk into the floppy drive
Enter DEBUG
-A 100
****: *100 MOV AL,0
****: **** MOV CX,1
****: **** MOV DX,0
****: **** MOV BX,1000
****: **** INT 25
****: **** INT 20
Press Enter
-G=0100

Insert the bad disk and enter Debug
-A 200
****: *100 MOV AL,1
****: **** MOV CX,1
****: **** MOV DX,0
****: **** MOV BX,1000
****: **** INT 26
****: **** INT 20
Press Enter
-G=200


### 5. Saving and Restoring CMOS Data
The 'address port' of CMOSRAM has an I/O port address of 70H, and the 'data port' has an I/O port address of 71H. When reading, just send the address of the CMOSRAM to be read to 70H, and then you can get the required data from 71H.

(1) Reading CMOS data Enter Debug
-A 100
****: *100 MOV BX,1000
****: **** MOV CX,0040
****: **** MOV AX,0000
****: 0109 MOV DX,CX
****: **** MOV CX,0005
****: 010E LOOP 010E
****: **** OUT 70,AL
****: **** MOV CX,0005
****: 0115 LOOP 0115
****: **** IN AL,71
****: **** MOV ,AL
****: **** CMP AH,0E
****: **** JB 0123
****: **** ADD AH,80
****: 0123 INC AH
****: **** INC BX
****: **** MOV CX,DX
****: **** MOV AL,AH
****: **** LOOP 0109
****: **** MOV AH,3C
****: **** MOV DX,0150
****: **** MOV CX,0020
****: **** INT 21
****: **** MOV BX,AX
****: **** MOV DX,1000
****: **** MOV CX,0040
****: **** MOV AH,40
****: **** INT 21
****: **** MOV AH,4C
****: **** INT 21
-A 150
****: 0150 DB "CMOS.DAT",0
****: 0159
-R CX
CX 0000
:60
-N SAVE CMOS.COM
-W
-Q
-W 100 2 0 1
-Q

(2) Restoring CMOS data Enter Debug
-A 100
****: *100 MOV CX,0150
****: **** MOV AH,3D
****: **** MOV AL,00
****: **** INT 21
****: **** MOV DX,1000
****: **** MOV BX,AX
****: **** MOV CX,0040
****: **** MOV AH,3F
****: **** INT 21
****: **** MOV AX,0000
****: **** MOV BX,DX
****: **** MOV DX,CX
****: **** MOV CX,0005
****: **** LOOP 011F
****: **** MOV AL,AH
****: **** OUT 70,AL
****: **** MOV CX,0005
****: **** LOOP 0128
****: **** MOV AL,
****: **** OUT 71,AL
****: **** JB 0136
****: **** ADD AH,80
****: **** INC AH
****: **** INC BX
****: **** MOV CX,DX
****: **** LOOP 011A
****: **** MOV AX,0040
****: **** MOV DS,AX
****: **** MOV AX,1234
****: **** MOV ,AX
****: **** JMP FFFF:0000
-A 150
****: 0150 DB "CMOS.DAT",0
****: 0159
-R CX
CX 0000
：60
-N WRITE CMOS.COM
-W
-Q


### 6. Saving and Restoring DOS Boot Sector Data
The DOS boot program is read and starts executing from memory 0000:7C00
Obtain the normal boot program
Enter Debug
-L 100 2 0 1
-N AOSBOOT.COM
-R CX
：200
-W
-Q

Load the boot program
Enter Debug
-N AOSBOOT.COM
-L
-R CX
：200
-W 100 2 0 1
-Q


### 7. Saving and Restoring Hard Disk Master Boot Sector Data
Read the master boot sector information when the hard disk is working normally
Note: This data cannot be used for restoration when the partition is changed
Save the master boot sector data Enter Debug
-A 100
MOV AX,0201
MOV BX,0110
MOV CX,0001
MOV DX,0080
INT 13
INT 3
-G=100
-E 102 3
-E 10E C3
-R BX
BX 0110
:0
-R CX
CX 0001
:210
-N A:RBOOT.COM
-W
-Q

Restore the master boot sector data: Just run RBOOT.COM on drive A


### 8. Backup and Restoration of Hard Disk Non-Allocation Table
Backup the allocation table when the computer is running normally
Enter Debug
-L 100 2 0 1
-N ABRUP.DAT
-R CX
：200
-W

Restore
Enter Debug
-N ABRUP.DAT
-L
-W 100 2 0 1
-Q


### 9. Inside Information of Hard Disk Protection Card
For people who often use computers outside, once the computer maintenance personnel set up a hard disk protection card, it is very troublesome to do some things by themselves. Do you want to shield the hard disk protection card? The following method may be referable:
Enter Debug
-A 100
MOV AH,0
MOV DL,0
INT 13
-T
Press T continuously until CS=F000, then record the value of DS at this time, such as: 1234
-E E0：4C
34 12 00 F0
-Q


### 10. Low-Level Formatting of Hard Disk with Debuf
Hard disk low-level formatting is generally done with DM, but DEBUG can also be used for low-level formatting of the hard disk
Enter Debug
-A 100
MOV AX,500
MOV BX,180
MOV CX,0
MOV DX,80
INT 13
INT 3
-E 180 0 0 0 2
-Q


### 11. Cold Boot and Hot Boot
Use DEBUG to implement system cold boot and hot boot programs

Cold boot:
-A 100
JMP FFFF:0
INT 20
-N A:RESET.COM
-R CX
：0007
-w
-Q

Hot boot:
-A 100
MOV AX,0040
MOV DS,AX
MOV AX,1234
MOV SI,0072
MOV (SI),AX
JMP FFFF:0
-N A:RSET.COM
-R CX
：0014
-W
-Q


### 12. Encryption of DOS Internal Commands
For example, encrypt dir
Find the COMMAND.COM file under C: with pctools or diskedit
Edit this file
In PCTOOLS: F-----F1 Then find all 03 44 49 52, and then press F5 to modify it to the value you want. For example: foo, then only by entering foo can the files or file directories be listed.
Diskfix has a good interface, and the operation is similar to pctools.
Note: If it cannot be modified, unlock the file's lock luck
Other command codes
type 04 54 59 50 45
cd 02 43 44
del 03 44 45 44
copy 04 43 49 50 59

I haven't seen these things for a long time, and there is a very familiar feeling.
Worth collecting

I feel the same!

Indeed, that's the case.

The several LOOPs in that program for reading CMOS look a bit strange. Who can explain their functions?

Thank you very much!!!

An expert!