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Document Title: [AtariVecInstructions.html (html file)]

Atari Analog Vector Generator Instruction Set 


Compiled from Atari schematics and specifications
Eric Smith  7/2/92
---------------------------------------------

NOTE: The vector generator is little-endian.  The instructions are 16 bit
      words, which need to be stored with the least significant byte in the
      lower (even) address.  They are shown here with the MSB on the left.

The stack allows four levels of subroutine calls in the TTL version, but only
three levels in the gate array version.

inst  bit pattern          description
----  -------------------  -------------------
VCTR  000- yyyy yyyy yyyy  normal vector
      zzz- xxxx xxxx xxxx
HALT  001- ---- ---- ----  halt - does CNTR also on newer hardware
SVEC  010y yyyy zzzx xxxx  short vector - don't use zero length
STAT  0110 ---- zzzz cccc  status
SCAL  0111 -bbb llll llll  scaling
CNTR  100- ---- dddd dddd  center
JSRL  101a aaaa aaaa aaaa  jump to subroutine
RTSL  110- ---- ---- ----  return
JMPL  111a aaaa aaaa aaaa  jump

-     unused bits
x, y  relative x and y coordinates in two's complement (5 or 13 bit,
      5 bit quantities are scaled by 2, so x=1 is really a length 2 vector.
z     intensity, 0 = blank, 1 means use z from STAT instruction,  2-7 are
      doubled
      for actual range of 4-14
c     color
b     binary scaling, multiplies all lengths by 2**(1-b), 0 is double size,
      1 is normal, 2 is half, 3 is 1/4, etc.
l     linear scaling, multiplies all lengths by 1-l/256, don't exceed $80
d     delay time, use $40
a     address (word address relative to base of vector memory)

Notes:

Quantum:
	the VCTR instruction has a four bit Z field, that is not
	doubled.  The value 2 means use Z from STAT instruction.

	the SVEC instruction can't be used

Major Havoc:
	SCAL bit 11 is used for setting a Y axis window.

	STAT bit 11 is used to enable "sparkel" color.
	STAT bit 10 inverts the X axis of vectors.
	STAT bits 9 and 8 are the Vector ROM bank select.

Star Wars:
	STAT bits 10, 9, and 8 are used directly for R, G, and B.