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 <ccth6...@gmail.com> Sent: 17 July 2023 06:24 To: r...@jarratt.me.uk; General Discussion: On-Topic and Off-Topic Posts <cctalk@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@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
