11 Mar
2017
11 Mar
'17
8:50 p.m.
On Sat, Mar 11, 2017 at 6:10 PM, Mouse via cctalk <cctalk at classiccmp.org> wrote:
It was 8-bit clean. And did allow for connection of a printer to it,
though a relatively simple one. We wound up in the end, though, not
using it except in a pinch. The limitations were just a bit too much
to give reliable behavior for anything other than having a DECwriter
II or VT220 connected to it.
We had a 4-port serial card to connect the plotter, and a few other
specialty devices we needed for our VaxStation II (which had the same
KA630 CPU board and a graphics board).
Warner
I'm not
sure about the MicroVax II but on some other VAX and Alpha
machines, the console port may be less capable than ordinary terminal
ports in the way of buffering, flow control, 8 bit support and so on.
The KA630, the MicroVAX-II CPU board (which includes the console serial
port), has a relatively limited serial port. For example, it has only
a byte or two of buffering in each direction, it cannot be used
directly from userland even if the kernel wants to let it (it is
accessed with MFPR and MTPR instructions), it has no software baudrate
control, and various other limitations.
These have concomitant benefits for console use, such as no software
setup being required to get small numbers of characters transferred.
But they do rather cripple it for voluminous data transfer. If you
have an at-least-mildly-smart serial port card (eg, with substantial
hardware buffering capability, and/or with DMA capability), you will
probably get better performance with it.