While it may be true that the Silabs parts are faster, since they don't allow external memory access, and, most of all, because they don't drop into a DIP40 socket, they don't fill all needs.

The DS89C4x0's allow execution rate changes, specifically, external memory cycle length changes, under software control. This means that I can execute code from internal flash at one rate, from external program space at a different rate, necessarily because of the address setup requirements, and accessing internal xdata memory at another rate. This is interesting in cases where the external memory map is used for slow peripherals, e.g. a 100 ns USB interface, and, as I'm presently studying, an FDC at ~400ns. Performance can be optimized by changing the cycle stretch factors under software control. Sadly, the MCU doesn't have a WAIT line, so synchronization with external hardware can be tricky.

I certainly agree with P. Gallo's comments about how page mode can be used, but it apparently isn't in wide use.

These MCU's are in full production, so they should be readily available.

The 2001 version of the 89C420 was troubled with a few bugs, the most notable of which was the inability to perform in-application programming of its flash memory. It was capable of being programmed with its bootloader, though, so no fancy programmer was needed. Also, it was readily capable of executing code at 50 MHz, though it was found that it could not reliably do so with code in its internal FLASH. If you load code into its 1KB internal XRAM, then reconfigure it so it's mapped into program space, you can run at full speed, though.

For me, the main benefit in these MCU's is the high speed, executing one instruction byte per clock tick, while residing on the standard 805x 40-pin DIP package. Running at 12x the "normal" rate while residing in the same physical hardware environment allows for lots of enhancements without any hardware mod's.

Those page modes interest me, since they permit faster execution from external memory, but (a) they require different hardware, since the address/data steering is different, and (b) I haven't seen lots of applications for the two page modes. I'm curious how, if at all, people have used these modes.

RE