Sinclair ZX80 / ZX81 / Z88 Forums

Having done the resistor thing mentioned in the other thread listed above I can confirm it works wonderfully, the only difference being the zeddy runs slightly slower at 60Hz.

Just to annoy Mark PAL PAL PAL PL PAL PAL PAL NTSC NTSC NTSC PAL PAL PAL!

Moggy wrote: Just to annoy Mark PAL PAL PAL PL PAL PAL PAL NTSC NTSC NTSC PAL PAL PAL!

Since "The Hitchhiker's Guide to the Galaxy" (resp. the German translation) "PAL" has a new meaning (at least in Germany): "Problem anderer Leute":
https://www.spreadshirt.de/pal+problem+ ... -A21425152

In English it is not NTSC, but SEP: https://en.wikipedia.org/wiki/Somebody_else%27s_problem

So if you install a PAL field generator next to the resistor, it is no more your problem

Siggi

Eines Tages werde ich verstehen, deutscher Humor.

Moggy wrote: ↑Mon Feb 20, 2017 1:42 pm Having done the resistor thing mentioned in the other thread listed above I can confirm it works wonderfully, the only difference being the zeddy runs slightly slower at 60Hz.

My lack of technical understanding will show up here, but why slower?
Aren't there 100 more lines to refresh in 50Hz mode and woudln't that affect anything?
I come from this in the Amiga world, where the PAL Amiga runs a tad faster clock wise (7.16 compared to 7.14), but programs (games) run faster on an NTSC Amiga (I was guessing because it had fewer lines to draw)???
Just wondering...
As I just got my USA model ZX81/TS1000 machines, I haven't had time to test any programs.
Are there many games that won't even run on a USA model (like the NTSC Amiga won't run a bunch of PAL games)?

Thanx!
(That also does make me wonder if I should put a switch (or can I re purpose the channel 3/4 switch after a composite mod) to flip from 50Hz/60Hz?)

As far as the computer logic side goes, the only significant difference between a 50Hz and a 60Hz screen display is the frequency of the system redrawing the video / TV screen. In a ZX80, ZX81, TS1000 and TS1500 the Z80 CPU actually gets the data from the memory for the ULA. The ULA converts the data from parallel form to a series of single bits suitable for forming into a video signal. By redrawing, I mean sending data from memory so that the video / TV display gets the required analogue signal so that a picture is displayed.

The same 6.5MHz clock oscillator is used regardless of which TV system is used. So the Z80 CPU runs at the same speed. Indeed in FAST mode, the speed of processing is about the same.

However, the more frequently the screen needs redrawing, the less time there is for the Z80 CPU to run your program. Because it is spending more time suppling screen data bytes to the ULA.

More complex computers have systems that generate and service the video or TV screen without the CPU being involved. For example, you can HALT the Z80 CPU in a ZX Spectrum and the display system will still produce a picture. If you HALT the Z80 CPU in a ZX80, ZX81, TS1000 or TS1500, the display will go blank (the same as using FAST mode).

Mark

Vertical Timings (50Hz)
Upper Blanking ..... 11592 cycles ..... 56 scanlines (7 charlines)
Display Area ........ 39744 cycles .... 192 scanlines (24 charlines)
Lower Blanking . ca.11592 cycles . ca. 56 scanlines (or a bit less)
Vertical Retrace ..... 1235 cycles .. ca. 6 scanlines

Vertical Timings (60Hz)
Upper Blanking ...... 6624 cycles ..... 32 scanlines (4 charlines)
Display Area ........ 39744 cycles .... 192 scanlines (24 charlines)
Lower Blanking . ca. 6624 cycles . ca. 32 scanlines (or a bit less)
Vertical Retrace ..... 1235 cycles .. ca. 6 scanlines

Above table taken from this web page.

The screen area usable by BASIC programs is the same. If a machine code program uses the ROM display system, the same applies. Only machine code programs that have their own video display system can have a different size area for picture information. Although apart from demos, the size if different is usually smaller.

Mark

Thanx for that info!!!
<voice in my head: Why don't you tell them that you don't understand what they said?>
<me: shut up.. I'll figure it out eventually.>

I’ve had that internal discussion going on for years now...

In all aspects of my life.

To put it another way...

<waits for confirmation that you want me to continue...>

Mark

OK...
After re-reading a bit:

The screen area usable by BASIC programs is the same. If a machine code program uses the ROM display system, the same applies.

I think I get it!!!!

Now it is making me think that if the monitor I plan on using these with is happy with 50Hz, I might convert my units to that.
(I can test that with my Amiga 1200.. I think I have used my 1200 on that monitor in PAL and it worked (in monochrome obviously) with some tweaking of the vertical hold, but that was a long time ago..)
And I might even look at a switch...
Of course, I have a lot to do just to get them working and happy before that, but it is tempting..

Thanx!