107



     To discover the exact end of memory, use this routine (it's a tad
     slow):

     10  RAMTOP = 106: TOP = PEEK(RAMTOP)
     20  BYTE = TOP * 256: TEST = 255 - PE
        EK(BYTE): POKE BYTE,TEST
     30  IF PEEK(BYTE) = TEST THEN TOP = T
         OP +1: POKE BYTE, 255 - TEST
     40  GOTO 20
     50  PRINT "MEMORY ENDS AT "; BYTE

     One caution: BASIC cannot always handle setting up a display
     list and display memory for GRAPHICS 7 and GRAPHICS 8
     when you modify this location by less than 4K (16 pages; 4096
     bytes). Some bizarre results may occur if you use PEEK(106) - 8
     in these modes, for example. Use a minimum of 4K (PEEK(106) -
     16) to avoid trouble. This may explain why some people have
     difficulties with player/missile graphics in the hi-res (high
     resolution; GR.7 and GR.8) modes. See location 54279 ($D407).

     Another alternative to reserving memory in high RAM is to save
     an area below MEMLO, location 743 ($2E7: below your BASIC
     program). See also MEMTOP, locations 741, 742 ($2E5, $2E6).

107            6B             BUFCNT
     Buffer count: the screen editor current logical line size counter.

108,109        6C,6D          BUFSTR
     Editor low byte (AM). Display editor GETCH routine pointer
     (location 62867 for entry; $F593). Temporary storage; returns the
     character pointed to by BUFCNT above.

110            6E             BITMSK
     Bit mask used in bit mapping routines by the OS display handler
     at locations 64235 to 64305 ($FAEB to $FB31). Also used as a
     display handler temporary storage register.

111            6F             SHFAMT
     Pixel justification: the amount to shift the right justified pixel data
     on output or the amount to shift the input data to right justify it.
     Prior to the justification process, this value is always the same as
     that in 672 ($2A0).

112,113        70,71          ROWAC
     ROWAC and COLAC (below) are both working accumulators for
     the control of row and column point plotting and the increment 
     and decrement functions.

114,115        72,73          COLAC
     Controls column point plotting.