User Commands - Commodore 1541 User Manual

> (HEXADECIMAL LOCATIONS)
USER COMMANDS
Aside from the USERl and USER2 commands discussed in chapter 6, and the
UI + and UI - commands in chapter 2, the USER commands are jumps to a table of
locations in the disk drive's RAM memory.
USER COMMAND FUNCTION
UI or UA BLOCK-READ without changing buffer-pointer
U2 or UB BLOCK-WRITE without changing buffer-pointer
U3 or UC jump to $0500
U4 or UD jump to $0503
U5 or UE jump to $0506
U6 or UF jump to $0509
U7 or UG jump to $050C
U8 or UH jump to $050F
U9 or UI jump to $FFFA
U; or UJ power-up vector
UI + set Commodore 64 speed
UI- set VIC 20 speed
By loading these locations with another jump command, like JMP $0520, you can
create longer routines that operate in the disk's memory along with an easy-to-use
jump table — even from BASIC!
EXAMPLES OF USER COMMANDS:
PRINT# 15, "U3"
PRINT# 15, "U" + CHR$(50+Q)
PRINT# 15, "UI"
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