CH_HLINE = 1
CH_VLINE = 2
-; huc6270 - Video Display Controller (vdc)
+; huc6270 - Video Display Controller (VDC)
VDC_MAWR = 0 ; Memory Address Write Register
VDC_MARR = 1 ; Memory Address Read Register
-VDC_VWR = 2 ; VRAM Write Register
-VDC_VRR = 3 ; VRAM Read Register
-VDC_CR = 4 ; Control Register
-VDC_RCR = 5 ; Raster Counter Register
-VDC_BXR = 6 ; Background X-Scroll Register
-VDC_BYR = 7 ; Background Y-Scroll Register
-VDC_MWR = 8 ; Memory-access Width Register
-VDC_HSR = 9 ; Horizontal Sync Register (?)
-VDC_HDR = 10 ; Horizontal Display Register (?)
-VDC_VPR = 11 ; (unknown)
-VDC_VDW = 12 ; (unknown use)
-VDC_VCR = 13 ; (unknown use)
-VDC_DCR = 14 ; (DMA) Control Register
-VDC_SOUR = 15 ; (DMA) Source Register
-VDC_DESR = 16 ; (DMA) Destination Register
-VDC_LENR = 17 ; (DMA) Length Register
-VDC_SATB = 18 ; Sprite Attribute Table
+VDC_VWR = 2 ; VRAM Write Register (write only)
+VDC_VRR = 2 ; VRAM Read Register (read only)
+VDC_UNK03 = 3 ; (unknown)
+VDC_UNK04 = 4 ; (unknown)
+VDC_CR = 5 ; Control Register
+VDC_RCR = 6 ; Raster Counter Register
+VDC_BXR = 7 ; Background X-Scroll Register
+VDC_BYR = 8 ; Background Y-Scroll Register
+VDC_MWR = 9 ; Memory-access Width Register
+VDC_HSR = 10 ; Horizontal Sync Register
+VDC_HDR = 11 ; Horizontal Display Register
+VDC_VPR = 12 ; Vertical synchronous register
+VDC_VDW = 13 ; Vertical display register
+VDC_VCR = 14 ; Vertical display END position register
+VDC_DCR = 15 ; (DMA) Control Register
+VDC_SOUR = 16 ; (DMA) Source Register
+VDC_DESR = 17 ; (DMA) Destination Register
+VDC_LENR = 18 ; (DMA) Length Register
+VDC_SATB = 19 ; Sprite Attribute Table
; VDC port
; Note: absolute addressing mode must be used when writing to this port