User Commands - Commodore 1541 User Manual

USER COMMANDS
Aside from the USER] 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
Ul orUA BLOCK-READ without changing buffer-pointer
U2 or UB BLOCK-WRITE without changing buffer-pointer
U3 or UC jump to 50500
U4 or UD jump to SO5O3
U5 or UE jump to $0506
U6 or UF jump to S05O9 HEXADECIMAL LOCATIONS)
U7 or UG jump to S050C
USorUH jumptoS050F
U9 or UI jump to SFFFA
U; or UJ power-up vector
UI+ set Commodore 64 speed
UI- set VIC 20 speed
By loading these locations with another jump command, lite JMP $0520, you can
create longer routines thai 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^+CHRStfO + Q)
PRINT* 15, "Ul"