MOS Technology 8563

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The 8563 Video Display Controller (VDC) was an integrated circuit produced by MOS Technology. It was used in the Commodore 128 computer to generate an 80-column (640×200 pixel) RGB video display, running alongside a VIC-II which supported Commodore 64-compatible graphics. The DCR models (as well as a few D-models) of the C128 used the later and more technically advanced 8568 [D]VDC controller.

History and characteristics[edit]

The VDC was designed with office suite applications in mind. Shown here is SpeedScript 128, a word processor.
This Ultra Hi-Res demo showcases the VDC's blitter capabilities with a simple 3D animation of a wire frame model of a cube.

Originally intended for a planned (but unreleased) UNIX-based business computer, Commodore designed the VDC into several prototype machines. Of these, only the Commodore 128 ever saw production. Unlike earlier MOS video chips such as the popular VIC-II, the VDC had dedicated video RAM, 16 kilobytes (upgradable to 64 kilobytes) in the original or "flat" C128 and 64 kilobytes in the C128DCR. This RAM was not directly accessible by the microprocessor.

The 8563 was more difficult to produce than most of the rest of the MOS Technology line, and initial yields were very low. [1] Also, there were timing issues with the VDC that would cause indirect load and store operations on its registers to malfunction.

Officially, the VDC was a text-only chip, although a careful reading of the technical literature by MOS Technology that was given to the early C128 developers did indicate that a high-resolution bitmap mode was possible—it simply wasn't described in any detail. BASIC 7.0, the Commodore 128's built-in programming language, only supported high-resolution graphics in 40-column mode via the legacy VIC-II chip.

Shortly after the release of the C128 the VDC's bitmap mode was described in considerable detail in a Data Becker book (published in late 1985 in the USA by Abacus Software), and an assembly language program was provided by the authors, in which it was possible to set or clear any pixel or, using BASIC to perform the necessary calculations, generate bitmapped geometric shapes on the 80 column screen. In February 1986, less than a year after the Commodore 128's release, RUN magazine published "Ultra Hi-Res Graphics", an article describing the VDC's bitmapped mode and including a type-in program (written in 8502 assembly language) that extended BASIC 7.0's capabilities to support 640×200 high-resolution graphics using the 8563. [2] Authors Lou Wallace and David Darus later developed the Ultra Hi-Res utility into a commercial package, BASIC 8. One of the most popular third-party utilities for the C128, this offered more advanced VDC high-resolution capabilities to a wide audience of programmers.

Commodore finally offered complete official documentation on the VDC in the Commodore 128 Programmer's Reference Guide. VDC bitmap modes were used extensively in the C128 version of the GEOS operating system.

The VDC lacked sprite capabilities, which limited its use in gaming applications. However, it did contain blitting capabilities to autonomously perform small block memory copies within its dedicated video RAM. While the VDC is performing such a copy, the system CPU can continue running code, provided no other VDC accesses are attempted before the copy is finished. These functions were used by the C128's screen editor ROM to rapidly scroll or clear screen sections.

Technical specifications[edit]

  • RGBI output (RGB plus Intensity) compatible with IBM's CGA video standard.
  • 16 or 64 kilobyte address space for display, character shape and display attribute memory (dedicated, separate from system memory).
  • Up to 720×700 pixel video resolution in interlaced mode (maximum with 64 kilobyte video ram) [3]. Other image sizes are possible, depending on programmer's needs, such as 640×200 non-interlaced, 640×400 interlaced, etc.
  • 80×25 characters text resolution (C128 kernel default); other sizes such as 80×50 or 40×25 are possible.
  • 8 colors at 2 intensities.

Programming[edit]

Addressing the VDC's internal registers and dedicated video memory must be accomplished by indirect means. First the program must tell the VDC which of its 37 internal registers is to be accessed. Next the program must wait until the VDC is ready for the access, after which a read or write on the selected internal register may be performed. The following code is typical of a register read:

        ldx #regnum       ;VDC register to access
        stx $d600         ;write to control register
loop    bit $d600         ;check bit 7 of status register
        bpl loop          ;VDC not ready
        lda $d601         ;read from VDC register
        ...

The following code is typical of a register write operation:

        ldx #regnum       ;VDC register to write to
        stx $d600         ;write to control register
loop    bit $d600         ;check bit 7 of status register
        bpl loop          ;VDC not ready
        sta $d601         ;write to VDC register
        ...

Owing to this somewhat cumbersome method of controlling the VDC, the maximum possible frame rate in bit-mapped mode is generally too slow for arcade-style action video games, in which bit-intensive manipulation of the display is required.

Register Listing[edit]

This information was adapted from the Commodore 128 Programmer's Reference Guide[1]

Register Hexadecimal Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Description
0
$00
HT7
HT6
HT5
HT4
HT3
HT2
HT1
HT0
Horizontal Total
1
$01
HD7
HD6
HD5
HD4
HD3
HD2
HD1
HD0
Horizontal Displayed
2
$02
HP7
HP6
HP5
HP4
HP3
HP2
HP1
HP0
Horizontal Sync Position
3
$03
VW3
VW2
VW1
VW0
HW3
HW2
HW1
HW0
Vertical/Horizontal Sync Width
4
$04
VT7
VT6
VT5
VT4
VT3
VT2
VT1
VT0
Vertical Total
5
$05
--
--
--
VA4
VA3
VA2
VA1
VA0
Vertical Adjust
6
$06
VD7
VD6
VD5
VD4
VD3
VD2
VD1
VD0
Vertical Displayed
7
$07
VP7
VP6
VP5
VP4
VP3
VP2
VP1
VP0
Vertical Sync Position
8
$08
--
--
--
--
--
--
IM1
IM0
Interlace Mode
9
$09
--
--
--
--
CTV4
CTV3
CTV2
CTV1
Character Total Vertical
10
$0A
--
CM1
CM0
CS4
CS3
CS2
CS1
CS0
Cursor Mode, Start Scan
11
$0B
--
--
--
CE4
CE3
CE2
CE1
CE0
Cursor End Scan Line
12
$0C
DS15
DS14
DS13
DS12
DS11
DS10
DS9
DS8
Display Start Address High Byte
13
$0D
DS7
DS6
DS5
DS4
DS3
DS2
DS1
DS0
Display Start Address Low Byte
14
$0E
CP15
CP14
CP13
CP12
CP11
CP10
CP9
CP8
Cursor Position High Byte
15
$0F
CP7
CP6
CP5
CP4
CP3
CP2
CP1
CP0
Cursor Position Low Byte
16
$10
LPV7
LPV6
LPV5
LPV4
LPV3
LPV2
LPV1
LPV0
Light Pen Vertical Position
17
$11
LPH7
LPH6
LPH5
LPH4
LPH3
LPH2
LPH1
LPH0
Light Pen Horizontal Position
18
$12
UA15
UA14
UA13
UA12
UA11
UA10
UA9
UA8
Update Address High Byte
19
$13
UA7
UA6
UA5
UA4
UA3
UA2
UA1
UA0
Update Address Low Byte
20
$14
AA15
AA14
AA13
AA12
AA11
AA10
AA9
AA8
Attribute Start Address High Byte
21
$15
AA7
AA6
AA5
AA4
AA3
AA2
AA1
AA0
Attribute Start Address Low Byte
22
$16
CTH3
CTH2
CTH1
CTH0
CDH3
CDH2
CDH1
CDH0
Character Total Horizontal, Character Display Horizontal
23
$17
--
--
--
CDV4
CDV3
CDV2
CDV1
CDV0
Character Display Vertical
24
$18
COPY
RVS
CBRATE
VSS4
VSS3
VSS2
VSS1
VSS0
Vertical Smooth Scrolling
25
$19
TEXT
ATR
SEMI
DBL
HSS3
HSS2
HSS1
HSS0
Horizontal Smooth Scrolling
26
$1A
FG3
FG2
FG1
FG0
BG3
BG2
BG1
BG0
Foreground/Background color
27
$1B
AI7
AI6
AI5
AI4
AI3
AI2
AI1
AI0
Address Increment per Row
28
$1C
CB15
CB14
CB13
RAM
--
--
--
--
Character Base Address
29
$1D
--
--
--
UL4
UL3
UL2
UL1
UL0
Underline Scan Line
30
$1E
WC7
WC6
WC5
WC4
WC3
WC2
WC1
WC0
Word Count
31
$1F
DA7
DA6
DA5
DA4
DA3
DA2
DA1
DA0
Data Register
32
$20
BA15
BA14
BA13
BA12
BA11
BA10
BA9
BA8
Block Start Address High Byte
33
$21
BA7
BA6
BA5
BA4
BA3
BA2
BA1
BA0
Block Start Address Low Byte
34
$22
DEB7
DEB6
DEB5
DEB4
DEB3
DEB2
DEB1
DEB0
Display Enable Begin
35
$23
DEE7
DEE6
DEE5
DEE4
DEE3
DEE2
DEE1
DEE0
Display Enable End
36
$24
--
--
--
--
DRR3
DRR2
DRR1
DRR0
DRAM Refresh Rate

References[edit]

  1. ^ Commodore Capital, Inc., (1986). Commodore 128 programmer's reference guide. New York, NY: Bantam Books, Inc.

External links[edit]


Video/sound chips from MOS Technology and second source/clone vendors

6545 CRTC6560 VIC6567 VIC-II6581 SID7360 TED8563 VDC8568 VDC