Commodore VIC-20 - Page 292

278 The VIC 20 User Guide
equivalent, 255. The number 65536 would then be stored into the
1540's memory as CHR$(255)CHR$(255). Any number
that can be
expressed in only one byte
(0 to 255) must be entered that way.
4. You must indicate how many bytes are being transferred. This
should also be expressed as hexadecimal numbers converted to
decimal notation, as above.
5. The MEMORY-WRITE instruction must be abbreviated "M-W".
No colon
or other punctuation is allowed.
The code, then, to store
255 into memory location 768 ($0300) is as
follows:
OPEN 15,8,15
PRINTI15,IM-W"CHR$(00)CHR$(03)CHR$(1)CHR$(255)
CLOSE 15
MEMORY-READ
It is possible to read any memory location in the 1540 using the
MEMORY-READ instruction. This instruction allows you to read one
byte at a time from the disk drive memory, similar to the way PEEK allows
you to read one byte at a time from the VIC 20's memory.
The BASIC instruction to read memory location 768 would be
PRINT PEEK(768)
The same instruction using the MEMORY-READ instruction would look
like this.
40 OPEN 15,8,15
50 PRINTtl15,IM-R"CHR$(00)CHR$(03)
60 GEnUS, A$
70 PRINT R.
8e CLOSE 15
This is what happened: First, we opened the command (error) channel
and then requested the MEMORY-READ instruction. On the same line
(with no additional punctuation) the byte to be read was specified (low byte
first, then high byte). This
is memory location 300-the same as 768
decimal.