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The special USER commands U1 (or UA) and U2 (or UB) can be used to replace
the BLOCK-READ and the BLOCK-WRITE commands.
The format for U1 is:
U1 forces the character count (buffer pointer) to 255 and reads an entire block
into memory. This allows complete access to all bytes in the block.
The format for U2 is:
U2 writes a buffer to a block on the disk without changing the contents of
position 0 as B-W does. This is useful when a block is to be read in (with B-R)
and updated (B-P to the field and PRINT#), then written back to diskette with
U2.
Refer to the random access example in Chapter 6 for an application of the U1
and U2 commands.
User
Designation
U1
U2
U3
U4
U5
U6
U7
U8
U9
U:
U3 through U9 commands are user defined. The locations jumped to are located
in the buffer areas of RAM and routines may be written to reside there and
uploaded using the M-W command.
48
"U1:"ch;dr;t;s
"U2:"ch;dr;t;s
Table 3
Alternate
User
Designation
UA
UB
UC
UD
UE
UF
UG
UH
UI
UJ
STANDARD JUMP TABLE
Function
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 $0065
power up vector
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