View source for Sprite port-mirror Attribute 2 (with INC) Register

{{NextRegister
|Number=$77
|Readable=No
|Writable=Yes
|ShortDesc=Same as {{NextRegNo|$37}} (write third byte of sprite-attributes), plus increments {{NextRegNo|$34}}
}}
Byte 3 is bitmapped:
{|class="wikitable"
! Bit !! Description
|-
| 4-7 || Palette offset, added to each palette index from pattern before drawing
|-
| 3 || Enable X mirror
|-
| 2 || Enable Y mirror
|-
| 1 || Enable rotation
|-
| 0 || MSB of X coordinate
|}

After write into sprite-attribute "byte 3" ({{PortNo|$xx57}}), the {{NextRegNo|$34}} is incremented (with all consequences stemming from such action). If the sprite 63 was modified, the result of the increment is officially "undefined behaviour", and code should explicitly set valid 0..63 sprite index before next sprite-attribute manipulation.