mirror of https://github.com/Klaus2m5/VTL02.git
69 lines
2.6 KiB
Plaintext
69 lines
2.6 KiB
Plaintext
-----------------------------------------------------
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VTL-2 for the 6502 (VTL02C)
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Original Altair 680b version by
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Frank McCoy and Gary Shannon 1977
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2012: Adapted to the 6502 by Michael T. Barry
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see source code for copyright notice
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Thanks to sbprojects.com for a very nice assembler!
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-----------------------------------------------------
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The basic concepts of VTL-2 (Very Tiny Language):
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http://www.altair680kit.com/manuals/Altair_680-VTL-2%20Manual-05-Beta_1-Searchable.pdf
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The files:
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Original source code from Mike:
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VTL02C for the apple II & the sbprojects.com assembler
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vtl02ca2.asm
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Modified versions (Syntax, I/O & user RAM size):
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VTL02C for the Kowalski 6502 simulator
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http://www.exifpro.com/downloads/6502_1.2.12.zip
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vtl02ca2.65s
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VTL02C for my emulator & the Kingswood AS65 assembler
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vtl02ca2.a65
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2015: Revision B included some space optimizations
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(suggested by dclxvi) and enhancements
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(suggested by mkl0815 and Klaus2m5):
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* Bit-wise operators & | ^ (and, or, xor)
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Example: A=$|128) Get a char and set hi-bit
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* Absolute addressed 8-bit memory load and store
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via the {< @} facility:
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Example: <=P) Point to the I/O port at P
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@=@&254^128) Clear low-bit & flip hi-bit
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* Starting with VTL02B, the space character is no
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longer a valid user variable nor a "valid" binary
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operator. It's now only significant as a numeric
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constant terminator and as a place-holder in
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strings and program listings, where it may be
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used to improve human readability (at a slight
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cost in execution speed and memory consumption).
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Example:
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* (VTL-2)
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1000 A=1) Init loop index
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1010 ?=A) Print index
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1020 ?="") Newline
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1030 A=A+1) Update index
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1040 #=A<10*1010) Loop until done
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* (VTL02B)
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1000 A = 1 ) Init loop index
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1010 ? = A ) Print index
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1020 ? = "" ) Newline
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1030 A = A + 1 ) Update index
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1040 # = A < 10 * 1010 ) Loop until done
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2015: Revision C includes further enhancements
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(suggested by Klaus2m5):
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* "THEN" and "ELSE" operators [ ]
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A[B returns 0 if A is 0, otherwise returns B.
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A]B returns B if A is 0, otherwise returns 0.
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* Some effort was made to balance interpreter code
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density with interpreter performance, while
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remaining within the 1KB constraint. Structured
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programming principles remained at low priority.
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