8 Jan
2001
8 Jan
'01
6:34 p.m.
On Jan 8, 22:33, Tony Duell wrote:
That's what most of the printer manuals I've
seen say as well -- get the
data stable for 0.5uS, bring stb/ low for 0.5us-1us (I saw the correction
you posted) and then keep the data stable for 0.5us after stb/ has risen
again.
Oh well... I'll try the falling edge (which is
what the majority of
machines use) and moan about machines that violate the (non-existant?)
standard.
The only genuine Centronics manuals I have are for the Centronics 737/739
printers, but for what it's worth, the technical section says the data must
be valid for 1us before the leading edge of the negative-going strobe
pulse, the pulse should last a minimum of 1us, and the data must remain
stable for 1us after the trailing (rising) edge. Of course, this isn't
necessarily a standard, just what one Centronics printer wants.
In this particular series, the BUSY signal goes active (high) on the
trailing edge of ~STROBE (within 50ns) and remains active until the leading
edge of ~ACKNLG (within 50ns); ~ACKNLG goes low (active) 300-470us after
the trailing edge of ~STROBE (or once the line is printed if the character
received is a CR), and lasts for 5us. The only other handshake is ~DEMAND,
which is the inverse of BUSY.
I used to have some Epson manuals, and I'm sure they use the leading
(negative-going) edge of ~STROBE as well.
--
Pete Peter Turnbull
Network Manager
Dept. of Computer Science
University of York