> From: Gooijen H
> To: "'info-pdp11@village.org'"
> Subject: RE: Input wanted: RX11 emulator (Unibus)
> Date: Wed, 13 Apr 2005 21:18:59 +0200
>
> That's a great idea, Carl. Nobody mentioned that before!
> M105's and the more modern M7821's are plenty available.
> So, there is no need to develop a dual-height board for that part!
> The device-specific board to be developed is then a "dual" instead
> of a "quad" sized one.
> I would have to look up the details, but I guess that your approach
> saves a few of the bus interface chips.
>
> - Henk, PA8PDP.
>
>
> --- Carl Lowenstein wrote:
> You can revert to the original intent of the SPC slot. M105 device
> selector and M782 interrupt controller in two of the slots, and the
> dual-height device-specific interface in the other two.
>
> Make a dual-height equivalent M105/M782 for half a project, and it
> will be re-usable for other things. Presumably could replace the
> real thing if somebody has lost their small cards.
>
> The interconnect between the device controller in CD, the M105 in E,
> and the M782 in F is already present in the SPC backplane.
>
Second thoughts on this -- the SPC slot when used in this way can not
do NPR (DMA) because back in 1970 there was no way to build a DMA
controller in such a small amount of real estate. So the signals
that would allow a device to become Bus Master are not processed by
the M782. But program-controlled data transfer is just fine.

carl
--
carl lowenstein marine physical lab u.c. san diego
clowenst@ucsd.edu
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