20 Jul
2023
20 Jul
'23
1:08 p.m.
Thanks for the suggestions but I think I was already aware of all of those. I have double
checked against your list and still don’t see the pulses with the DSO. There has to be
something else I am doing wrong ☹
From: Tom Hunter <ccth6600(a)gmail.com>
Sent: 17 July 2023 06:24
To: rob(a)jarratt.me.uk; General Discussion: On-Topic and Off-Topic Posts
<cctalk(a)classiccmp.org>
Subject: Re: [cctalk] Re: VT100: Datasheet for Intel 8228
Common DSO trigger problems experienced by a novice are:
1) Trigger position is off the screen. The trigger position relative to the current
visible capture is typically shown somewhere on the screen - often at the top of the
screen. Reduce the horizontal resolution to something like 10 ms/division and then scroll
the trigger position to be in the exact centre of the screen and then increase the
horizontal resolution to something suitable e.g 500 ns/division. Typically the DSO will
keep the trigger position centred if you had it close enough to the centre position before
increasing the horizontal resolution.
2) The horizontal resolution is set so that the pulse is invisible. For example 1
ms/division for a 10 ns pulse.
3) Triggering on the wrong channel.
4) Trigger level above or below the signal.
5) Trigger mode set to "Auto" as opposed to "Normal" or
"Single" causing a momentary display of the triggered signal which is
immediately overwritten by the current signal.
Tom Hunter
On Mon, Jul 17, 2023 at 1:14 AM Rob Jarratt via cctalk <cctalk(a)classiccmp.org
<mailto:cctalk@classiccmp.org> > wrote:
I used a logic analyser to check the 8228 and it does appear to be working as expected as
can be seen here https://rjarratt.files.wordpress.com/2023/07/8228-operation.jpg. The
labels are not very clear, but the 3rd from top is the WR input and the 4th from top is
the I/O W output. So it does look like it is working.
The odd thing is that I can't pick this up with my DSO. I have tried messing with the
trigger, but I just can't pick up anything that shows I/O W going low. I am using -ve
edge triggers. I have tried a pulse trigger with a width >20ns and I have tried nth
edge trigger, neither of the latter two ever trigger. Obviously it is my method that is
wrong, but I really don't know what it is about my method that is wrong. Are there any
common mistakes that novices make?
Thanks
