Port 3CF, 01  -  Enable Set/Reset register

        1111 xxxx  Reserved
        xxxx 1xxx  Enable Set/Reset Map 3
        xxxx x1xx  Enable Set/Reset Map 2
        xxxx xx1x  Enable Set/Reset Map 1
        xxxx xxx1  Enable Set/Reset Map 0

        Bits 3-0:  Those bits enable the set/reset function used when
                   write mode 0 is selected in register 3CF, 05. When
                   the bit is set to 1, the respective memory map
                   receives the value specified in the Set/Reset
                   register. When Set/Reset is not enabled for a map,
                   that map receives the value sent by the system.