FNAM_BANK := $C7 ; Bank for filename
KEY_COUNT := $D0 ; Number of keys in input buffer
FKEY_COUNT := $D1 ; Characters for function key
-MODE := $D7 ; 40/80 column mode flag
+MODE := $D7 ; 40-/80-column mode (bit 7: 80 columns)
CURS_X := $EC ; Cursor column
CURS_Y := $EB ; Cursor row
SCREEN_PTR := $E0 ; Pointer to current char in text screen
; ---------------------------------------------------------------------------
; I/O: VDC (128 only)
-VDC_INDEX := $D600
-VDC_DATA := $D601
+VDC_INDEX := $D600 ; register address port
+VDC_DATA := $D601 ; data port
+
+; Registers
+VDC_DATA_HI = 18 ; video RAM address (big endian)
+VDC_DATA_LO = 19
+VDC_CSET = 28
+VDC_RAM_RW = 31 ; RAM port
; ---------------------------------------------------------------------------
; I/O: Complex Interface Adapters