DMA Units
A MultiCam channel needs one or two digitizing unit(s) to transfer the camera video data into an single well-organized array of the frame buffer area.
There can be up to two cameras working simultaneously, consequently there are up to two image arrays defined inside the frame buffer.
The rationale for a PC based frame grabber is to transfer the camera picture into the PC memory. To efficiently achieve this goal, the Alpha board incorporates two independent DMA machines able to simultaneously and independently transport the frame buffer data into two PC memory surfaces.
DMA means "Direct Memory Access". This means that the data transfer is done through the PCI bus without intervention of the PC CPU.
Because of the total independence and programmability of each device participating at carrying the images from the camera to the PC memory, including the DMA machines, the Alpha board is effectively a double frame grabber on one printed circuit board.
It is conceptually adequate to associate one DMA unit to one camera connector. Consequently, the DMA units are referred to by X and Y.
The following block diagram helps to visualize the concept.
DMA units