The setup times, the times to refill the FIFOs, the time to arbitrate, etc., are all taken into account. Then take a careful look at this number. If this number is greater, you have excess bus time to do other things, such as image processing analyses. Obviously, this was below the required RS170 rates, so if anyone wanted to achieve respectable transfer rates, they had to use on-board memory. Unfortunately, some of these opportunities create confusion in the customer as less than the full story is told concerning data transfer rates with only a FIFO buffer present.
Cost Let's take a closer look at the issues.
The first thing to consider is cost-frame grabbers without memory cost less than those with memory. Consequently, frame grabbers with on-board memory will cost a bit more than those without. Bus Mastering A second issue to consider is whether or not the frame grabber has bus mastering capabilities. The PCI bus is efficient enough that you can transfer data from the frame grabber to host memory by having the CPU control the data movement. Unfortunately, this hogs processor time and turns your CPU into an expensive address generator.