Commodore 1541 - Programming the Disk Controller; Memory-Read

8. PROGRAMMING THE DISK CONTROLLER
The expert programmer can actually design routines that reside and operate on the
disk
controller. DOS routines can be added that come from The diskette. Routines can
be added much the same way as the DOS Support Program is "wedged" into your
memory.
BLOCK-EXECUTE
This command will load a block from the diskette containing a machine language
routine, and begin executing it at local ion 0 in the buffer until a RTS (ReTurn from
Subroutine) command is encountered.
FORMAT FOR BLOCK-EXECUTE:
PRINTflfiletf, "B-E:" channel- drive; track; block
MEMORY-READ
There is !6K of ROM in the disk drive as well as 2K of RAM. You can get direct
access to these, or to the buffers that the DOS has set up in the RAM, by using the
MEMORY commands. MEMORY-READ allows you to select which byte to read,
through (he error channel.
FORMAT FOR MEMORY-READ:
, H1M-R" CHRSflow byte of address) CHR5(high byte)
(no abbreviation!)
The next byte read using the GETtf statement through channels 15, the error
channel, will be from that address in the disk controller's memory, and successive bytes
will be From successive memory locations,
Any INPUTS to the error channel will give peculiar results when you're using this
command. This can be cleared up by any other command to the disk (aside from a
memory command).
PROGRAM TO READ THE DISK CONTROLLER'S MEMORY:
10
20
25
30
40
jyJ
60
70
so
90
100
]10
OPEN15,8,15
INPUT"LOCATION PLEASE";A
FOR L=lTO50
Al = INT(A/256): A2= A - A 1*256
PRINT#15,4'M-R"CHRS(A2)CHRS(A1)
OtlffljfAl — _^^
PRINT ASC(A$ + CHRS(0));
A=A+ 1
NEXT
INPUT "CONT1NUE";AJ
IF LEFTS(AIJ) = "Y>r THEN 25
GOTO20
/GET CHARACTERS
~\ FROM ERROR
\ CHANNEL }
45