[cctalk] Re: 14 DZ11's for sale/whatever

[Paul Koning via cctalk]

> On Oct 30, 2022, at 2:49 PM, Wayne S via cctalk <cctalk@classiccmp.org> wrote:
> 
> The difference between dz and dh interfaces is that the dh used dma instead 
> of interrupts to get characters to the cpu. It would be transparent to any 
> software.

No, it doesn't.  I was confused about this but was recently corrected.

The DH11 does DMA output, but not DMA input.  I don't know any DEC serial port 
devices that have DMA input; it would make very little sense to do that since 
input generally is one character at a time.  Block mode terminals do exist in 
DEC's world but they are rare, and even those are hard to operate with simple 
DMA.

DZ is programmed I/O in both directions, which makes the difference.  In 
typical usage, the bulk of the terminal traffic is output, so doing that with 
DMA is a big win.

        paul