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NOTES.VAN
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TITLE SECRETS OF CP/M VERSION 1.4
FILENAME SECRET14.DOC
AUTHOR Robert A. Van Valzah 4/27/78
M Y S T E R Y B D O S F U N C T I O N S
FUNC ACTION
---- ------
28 MAKE CURRENT DRIVE READ ONLY (R/O)
29 RETURN R/O VECTOR. RETURNS A BYTE VALUE (IN REG A)
WITH A "1" IN BIT POSITIONS OF R/O DISKS, LEAST
SIGNIFICANT BIT CORRESPONDING TO DRIVE A.
30 SET DIRECTORY I/O DMA ADDRESS. INITIALLY SET TO 80H.
DISK DATA I/O CONTINUES AT THE LAST ADDRESS SET BY
FUNCTION 26.
B O O T A N D G O M O D F O R C C P
There are some dedicated CP/M applications where it
would be nice if a cold start would load CP/M and then load a
transient and give it control. This could be used to make a
disk which would always power up in BASIC, for instance. This
capability has been built into CP/M version 1.4.
THEORY
------
When the CCP is loaded, it checks its console input
buffer to see if a command is waiting. As supplied by Digital
Research, this buffer is empty and the CCP simply signs on and
prompts the user for input. The task at hand, therefore, is to
fill this buffer so its contents will be executed as a CCP
command as the CCP is loaded. Assuming you have SID and desire
a command length of <=16 characters, this is quite simple:
1) Load an image of your operating system into low memory
(ready for SYSGEN). EX: SID CPMnn.COM
2) Type "I" followed by the command line as you like CCP
to execute it. EX: ISTAT.COM
3) Type M80,90,987
4) Boot and SYSGEN a disk in the normal manner.
The disk will now boot and execute the command typed
in step 2 above.
If you don't have SID or desire a command line longer
than 16 characters:
1) Perform step 1 above (use DDT if needed).
2) Patch the length of your command into location 987H.
3) Patch the ASCII of the command into memory starting at
location 988H, following it with the Digital Research
copyright message "COPYRIGHT (C) 1978, DIGITAL
RESEARCH ".
4) Perform step 4 above.