Commodore 1581 - User Commands; Utility Loader

User Command
U0
u0 + (cmd)
ul or ua
u2 or ub
u3 or uc
u4 or ud
u5 or ue
u6 or uf
u7 or ug
u8 or uh
u9 or ui
u: or uj
Function
restores default user jump table
burst utility command
(see Chapter 9 Burst Commands)
block read replacement
block write replacement
jump to $0500
jump to $0503 .
jump to $0506
jump to $0509
jump to $050c
jump to $050f
jump to ($fffa) reset tables
power up vector
By loading these memory locations with another machine lan
guage JMP command, such as JMP $0520, you can create longer rou
tines that operate in the disk's memory along with an easy-to-use jump
table.
FORMAT FOR USER COMMANDS:
PRINT#15,"Ucharacter";
where "character" defines one of the preset user commands listed
above.
EXAMPLES:
PRINT#15,"U:"; Form of DOS RESET command
PRINT#15,"U3"; Execute program at start of buffer 2
UTILITY LOADER
This command loads a user-type (USR) file into the drive RAM.
The first two bytes of the file must contain the low and high addresses
respectively. The third byte is the amount of characters to follow. In
addition, a trailing checksum byte must be included. The load address
is the starting address.
FORMAT FOR THE UTILITY LOADER COMMAND
PRINT#15,u&0:filename"
To return from this routine, the program should end with an RTS.
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