1 Nov
2022
1 Nov
'22
5:05 p.m.
Sent from my iPhone
On Nov 1, 2022, at 10:01, Wayne S
<wayne.sudol(a)hotmail.com> wrote:
Hi Paul. Who “corrected” you about DMA input? I’d like to read about that as nothing i
read about the DZ mentioned that. Got any Cites?
Sent from my iPhone
> On Nov 1, 2022, at 09:01, Paul Koning via cctalk <cctalk(a)classiccmp.org>
wrote:
>
>
>
>>> On Oct 30, 2022, at 2:49 PM, Wayne S via cctalk <cctalk(a)classiccmp.org>
wrote:
Also, can you define what the phrase “programmed io” refers?
AFAIK, pretty much everything does that, so a clarification would help.
>
>> 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
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>