1 Nov
2022
1 Nov
'22
4 p.m.
On Oct 30, 2022, at 2:49 PM, Wayne S via cctalk
<cctalk(a)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