On Jun 26, 2021, at 7:08 PM, Maciej W. Rozycki
<macro at orcam.me.uk> wrote:
On Fri, 25 Jun 2021, Paul Koning via cctalk wrote:
Well you
can find mother boards with real COM port, but they are rare.
One place you can find them easily is on industrial computers. My
firewall machine is one, because I wanted it to be fanless. It has the
usual pile of USB ports and HDMI, but also 2 COM ports; another model of
that same line has 6 COM ports.
What seems to be harder to find is a parallel printer port, but there is
far less reason to want one of those.
However both serial and parallel ports remain reasonably available as
PCIe option devices. Though parallel ports seem to be made as legacy PCIe
devices only, that is accessed with I/O rather than memory read/write bus
cycles, which are not, as I have learnt the hard way recently, supported
by all computer systems nowadays. I guess x86 systems will continue to
support them however as x86 CPUs have native I/O access instructions.
I/O cycles on PCI have no direct connection to I/O instructions. I've routinely used
I/O operations in PCI on a MIPS platform, which of course has no such concept; all that
was needed is to send the memory cycles to the address block that the PCI bridge maps onto
I/O cycles rather than memory cycles.
paul