REU & 2MHz?

[commodorejohn]

Here's a question. I know that, when the 128 runs in 2MHz mode, it clock-stretches most I/O accesses to 1MHz. Does this include the REC registers for a 1700 or 1750 REU? And, more importantly, does this extend to the DMA transfers to and from an REU?

[Hydrophilic]

I don't have an REU to test this, but if you believe the C128 Schematics in the PRG, then the answer is yes, I/O access to REC registers and DMA transfers occur at 1MHz.  The 2MHz line does not go to the expansion port.

It might be possible to build a device that operates at 2MHz by watching the DOT CLOCK which is present on the expansion port and runs at 8MHz.  This would require dividing down to 2MHz and synchronizing with 1MHz clock.

Or maybe not... although I can't find it at the moment, I thought the PRG said memory runs at 1MHz whenever DMA is asserted, which is true for the REC to control the data/address busses.

[commodorejohn]

Ah, that's kind of what I expected. Thanks!