Author: Andrew W (220.127.116.11)
Date: 09-17-2002 21:17
It has been years since I've used the Motorola 56k, but this is what I remember off the top of my head...
The DSP56k has what's called a Harvard architecture (rather than a conventional, Von Neuman architecture?), which means that it has multiple memory busses. This is useful for DSPs, which generally require high-speed data throughput and very fast multiply-accumulate cycles. Internally, the chip actually has three separate 24-bit busses: X (X data), Y (Y data), and P (program). Externally these busses are mapped onto a single bus, and two extra pins, X/Y and P, are used by the DSP to signal which external memory map it's trying to access. These extra pins can be viewed as simply extra address pins - e.g., A16 and A17 - though in the case that P is asserted, X/Y is ignored.
Feel free to email me if you have any questions. I don't own a Falcon, so I don't normally peruse this discussion board. I'm happy to participate, however, if a discussion about the DSP takes off...
-andrew (andrew1_remote at hotmail - just remove the 1 from the username!)