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Very Tiny Language for the 6502 series of CPUs
fbd001c897
; added inline divide by 10 to prnum:.
; fixed statement delimiter not overriding mismatched
; parentheses.
; line numbers >= 65280 are now reserved for the
; following fast return & goto features.
; added a gosub stack, depth = 16 address words.
; {==...} is a gosub and pushes the return address
; of the next line.
; {#==} is a return and pops the address when the
; result is the special line numer asigned to {=}.
; added a 31 line addresses acronym label array.
; lowercase characters and symbols in the $60-$7e
; range are used to address the array. the array
; is populated with the address of a line when a
; character in the allowed range preceeds the line
; number.
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| vtl02ca2.asm | ||
| vtl02sg.a65 | ||
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VTL-2 for the 6502 (VTL02C)
Original Altair 680b version by
Frank McCoy and Gary Shannon 1977
2012: Adapted to the 6502 by Michael T. Barry
see source code for copyright notice
Thanks to sbprojects.com for a very nice assembler!
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The basic concepts of VTL-2 (Very Tiny Language):
http://www.altair680kit.com/manuals/Altair_680-VTL-2%20Manual-05-Beta_1-Searchable.pdf
The files:
Original source code from Mike:
VTL02C for the apple II & the sbprojects.com assembler
vtl02ca2.asm
Modified versions (Syntax, I/O & user RAM size):
VTL02C for the Kowalski 6502 simulator
http://www.exifpro.com/downloads/6502_1.2.12.zip
vtl02ca2.65s
VTL02C for my emulator & the Kingswood AS65 assembler
vtl02ca2.a65
VTL02C codename "Speedy Gonzales"
vtl02sg.a65
this is a work in progress version and is my attempt
to trade performance versus codesize
2015: Revision B included some space optimizations
(suggested by dclxvi) and enhancements
(suggested by mkl0815 and Klaus2m5):
* Bit-wise operators & | ^ (and, or, xor)
Example: A=$|128) Get a char and set hi-bit
* Absolute addressed 8-bit memory load and store
via the {< @} facility:
Example: <=P) Point to the I/O port at P
@=@&254^128) Clear low-bit & flip hi-bit
* Starting with VTL02B, the space character is no
longer a valid user variable nor a "valid" binary
operator. It's now only significant as a numeric
constant terminator and as a place-holder in
strings and program listings, where it may be
used to improve human readability (at a slight
cost in execution speed and memory consumption).
Example:
* (VTL-2)
1000 A=1) Init loop index
1010 ?=A) Print index
1020 ?="") Newline
1030 A=A+1) Update index
1040 #=A<10*1010) Loop until done
* (VTL02B)
1000 A = 1 ) Init loop index
1010 ? = A ) Print index
1020 ? = "" ) Newline
1030 A = A + 1 ) Update index
1040 # = A < 10 * 1010 ) Loop until done
2015: Revision C includes further enhancements
(suggested by Klaus2m5):
* "THEN" and "ELSE" operators [ ]
A[B returns 0 if A is 0, otherwise returns B.
A]B returns B if A is 0, otherwise returns 0.
* Some effort was made to balance interpreter code
density with interpreter performance, while
remaining within the 1KB constraint. Structured
programming principles remained at low priority.