System Specification for C65: System Hardware - The CSG 4567 System/Video Controller

System Specification for C65

Fred Bowen

March 1, 1991

DMA and special CPU Accesses

VMF -- Video Matrix Fetch: The 4567 performs Video Matrix Fetches, during displayed video times, in all of the original VIC-II modes (SCM, MCM, ECM, BMM) . This is true for both 40 and 80 column (320 and 640 pixel) modes. During VMF, the 4567 reads both banks (A & B) of memory over both data busses D0-D7 and E0-E7. The D0-D7 bus provides the video matrix data, E0-E3 provides color data, and E4-E7 provides character attribute data.
CDF -- Character Data Fetch: The 4567 performs Character Data Fetches immediately after each Video Matrix Fetch in the original VIC-II modes except bitmap mode. During this fetch Character image data is fetched from ROM or RAM bank A over the D0-D7 bus.
BMF -- BitMap Fetch: The 4567 performs Bitmap Data Fetches immediately after each video Matrix Fetch, only in the bitmap mode. During this fetch, Bitmap image data is fetched from RAM bank A over the D0-D7 bus.
BPF -- Bitplane Fetch: The 4567 can perform Bitplane image fetches during displayed video times, if the Bitplane mode (BPM) is enabled. The number and position of these fetches is determined by which bitplanes are enabled. During bitplane fetches, even numbered bitplane data is fetched over DO-D7 and odd numbered bitplane data is fetched over E0-E7.
RF -- RAM refresh: The 4567 performs six cycles of dynamic RAM refresh every scanned video line. During this time no data is fetched and CASA* and CASB* are not activated.
SPF -- Sprite Pointer Fetch: Up to eight Sprite Pointer Fetches can occur each scanned video line. One SPF is generated for each sprite that is enabled and currently being displayed. During an SPF, the pointer to the sprite image data is fetched from the video matrix area of memory for the sprite in question over the D0-D7 data bus.
SDF -- Sprite Data Fetch: Three Sprite Data Fetches follow each Sprite Pointer Fetch. During this time, sprite image data for the sprite in question is fetched over the D0-D7 data bus.
DAT -- Display Address Translation: Display Address Translation, or DAT fetches, are not actually DMA-type accesses, but rather CPU address redirections to RAM. In this case, the unmultiplexed address bus is totally separated from the multiplexed address bus.
COL -- Color RAM accesses: Color RAM is also accessed by the CPU via an address translation. This is because color RAM would otherwise be located in the I/O area.

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