Just for fun, I added a buffer indicator to the ap2000. The buffer size is shown by the little green bars in the upper left of the printout. Each bar represents a hex digit of the size. It's kinda fun to watch the bars grow and shrink as the buffer fills and clears.

It's also a good indicator of whether the system is properly respecting the busy/ack signals as it will never use the buffer if so.

[Linked Image from i.imgur.com]