11/45 progress

[Paul Koning]

>>>>> "Jay" == Jay West <jwest at classiccmp.org> writes:

 Jay> You wrote...
 >> It's a UART.  Unless you wire it for loopback, you normally won't
 >> read back the same data you wrote.
 Jay> Yeah, it's a UART. But I assumed you wrote data to a register,
 Jay> then wrote data to a different register to strobe the data out,
 Jay> etc. So I figured the first register was just a temporary buffer
 Jay> that would hold it's contents until replaced by data in the
 Jay> opposite direction. My bad.

DEC UARTs have a receive and a transmit register.  Receive is
read-only, of course.  Transmit could be write-only or read-write.  I
would have expected read-write.  Usual practice was to make things
read-write if they had to be writeable, as an aid to diagnostics.
Write-only registers are a real pain for diagnostics writers because
you can't tell if the bits are working, so DEC avoided them as a
normal design practice.

       paul