VTL02C

update to VTL02C

readme.txt

@@ -1,28 +1,30 @@
 -----------------------------------------------------
-             VTL-2 for the 6502 (VTL02B)             
+             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! 
 -----------------------------------------------------
- 2015: Revision B, with several space optimizations
-   (suggested by dclxvi) and enhancements (suggested
-   by mkl0815 and Klaus2m5).
 
  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:
-   VTL02B for the apple II & the sbprojects.com assembler:
-      vtl02ba2.asm
-   VTL02B for the Kowalski 6502 simulator: 
-   http://www.exifpro.com/downloads/6502_1.2.12.zip:
-      vtl02ba2.65s
-   VTL02B for my emulator & the Kingswood AS65 assembler:
-      vtl02ba2.a65
+   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
  
- New features in Revision B:
+ 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
 
@@ -31,13 +33,13 @@
    Example:  <=P) Point to the I/O port at P
              @=@&254^128) Clear low-bit & flip hi-bit
 
- * The space character is no longer a valid user
-     variable nor a "valid" binary operator.  It is
-     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.
+ * 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
@@ -52,3 +54,15 @@
        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.