| BIT#  | FUNCTION                   |
          | 15    | (unused)                   |
          | 14    | HARDDIS                    |
          | 13    | LPENDIS                    |
          | 12    | VARVBEN                    |
          | 11    | LOLDIS                     |
          | 10    | CSCBEN                     |
          | 9     | VARVSYEN                   |
          | 8     | VARHSYEN                   |
          | 7     | VARBEAMEN                  |
          | 6     | DUAL                       |
          | 5     | PAL                        |
          | 4     | VARCSYEN                   |
          | 3     | (unused, formerly BLANKEN) |
          | 2     | CSYTRUE                    |
          | 1     | VSYTRUE                    |
          | 0     | HSYTRUE                    |

HARDDIS = This bit is used to disable the hardwire vertical horizontal window limits. It is cleared upon reset.
LPENDIS = When this bit is a low and LPE (BPLCON0,BIT 3) is enabled, the light-pen latched value(beam hit position) will be read by VHPOSR, VPOSR and HHPOSR. When the bit is a high the light-pen latched value is ignored and the actual beam counter position is read by VHPOSR, VPOSR, and HHPOSR.
VARVBEN = Use the comparator generated vertical blank (from VBSTRT, VBSTOP) to run the internal chip stuff-sending RGA signals to Denise, starting sprites,resetting light pen. It also disables the hard stop on the vertical display window.
LOLDIS = Disable long line/short toggle. This is useful for DUAL mode where even multiples are wanted, or in any single display where this toggling is not desired.
CSCBEN = The variable composite sync comes out on the HSY pin, and the variable conosite blank comes out on the VSY pin. The idea is to allow all the information to come out of the chip for a DUAL mode display. The normal monitor uses the normal composite sync, and the variable composite sync &blank come out the HSY & VSY pins. The bits VARVSTEN & VARHSYEN (below) have priority over this control bit.
VARVSYEN= Comparator VSY -> VSY pin. The variable VSY is set vertically on VSSTRT, reset vertically on VSSTOP, with the horizontal position for set set & reset HSSTRT on short fields (all fields are short if LACE = 0) and HCENTER on long fields (every other field if LACE = 1).
VARHSYEN= Comparator HSY -> HSY pin. Set on HSSTRT value, reset on HSSTOP value.
VARBEAMEN=Enables the variable beam counter comparators to operate (allowing diffrent beam counter total values) on the main horiz counter. It also disables hard display stops on both horizontal and vertical.
DUAL = Run the horizontal comparators with the alternate horizontal beam counter, and starts the UHRES pointer chain with the reset of this counter rather than the normal one. This allows the UHRES pointers to come out more than once in a horizontal line, assuming there is some memory bandwidth left (it doesn`t work in 640*400*4 interlace mode) also, to keep the two displays synced, the horizontal line lengths should be multiples of each other. If you are amazingly clever, you might not need to do this.
PAL = Set appropriate decodes (in normal mode) for PAL. In variable beam counter mode this bit disables the long line/short line toggle- ends up short line.
VARCSYEN= Enables CSY from the variable decoders to come out the CSY (VARCSY is set on HSSTRT match always, and also on HCENTER match when in vertical sync. It is reset on HSSTOP match when VSY and on both HBSTRT & HBSTOP matches during VSY. A reasonable composite can be generated by setting HCENTER half a horiz line from HSSTRT, and HBSTOP at (HSSTOP-HSSTRT) before HCENTER, with HBSTRT at (HSSTOP-HSSTRT) before HSSTRT. HSYTRUE, VSYTRUE, CSYTRUE = These change the polarity of the HSY*, VSY*, & CSY* pins to HSY, VSY, & CSY respectively for input & output.
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