Use of FAST mode... for typing?

[colinhoad]

I was reading my ZX81 manual and enjoyed learning about the FAST and SLOW modes. It's adorable, genuinely. However, this line from the manual, regarding reasons to use FAST mode, has got me confused:

"...you are typing in a long program. You will already have noticed how the listing gets remade every time you enter a new program line, & this can get annoying."

Did the manual's author really think that having the program listing redrawn after each line was *more* annoying than having every single keystroke causing the screen to blink? If you're in FAST mode, that's the effect... so I am struggling to understand why "typing in a long program" would be a reason to put the machine into FAST mode! Did I miss something?

[Paul]

Very easy: the longer the line becomes the more annoying it is to wait for the redraw of the line before typing the next character.
In fast mode you can keep typing and don't have to watch the screen while typing because the flickering can be recognised without watching the screen.
That makes typing much quicker.
Just try it out.
Make a long print statement with more than four lines of text

[colinhoad]

Thank you for the explanation! I did try it out, although I think because my ZX81 is outputting via a SCART composite lead, the total screen blackout after every keystroke in FAST mode (as the TV attempts to re-identify the SCART source) undermines the effect you are describing. I suspect the original UHF connection would have behaved differently, and so it's still useful to understand where the manual's author was coming from! Thanks again for clarifying

[1024MAK]

That's an effect of the automatic input selection (on the SCART) system.
When the ZX81 was designed and manufactured, it was intended to be used with the CRT TV's of the day. Which typically only had an aerial input socket.

Even when TV's started to get SCART sockets, they mostly had manual input selection (typically either via a menu of via an AV input selection button on the remote control or on the TV itself).

Mark

[colinhoad]

Thanks, Mark - that tallies up with what I'm seeing and makes perfect sense. If I had more space I'd probably look at getting a CRT (both for my ZX81 and my Beeb) but for now my trusty Sharp TV flatscreen will have to see me through - at least it still has a SCART socket, even those are a rarity nowadays!

[1024MAK]

It should also be noted that most modern TVs, including the later CRT models, also added 'no signal' detection. Then, when the display cannot detect a valid sync it switches to an internally generated 'no signal' picture.

Rather confusingly, this 'feature' may work differently on different inputs of the same TV, as well as between different brands/models/makes.

Someone created an extra circuit that takes the composite video from the ZX81 and automatically adds the missing sync pulses when the ZX81 does not provide them. Hence preventing the TV from switching between inputs or showing the 'no signal' picture.

However, I can't remember where I saw this project

Mark