PAL vs NTSC systems

[Kweepa]

As Boray alluded to, in PAL machines the CPU is clocked very slightly faster.

[TLovskog]

I thought the 50Hz update rate of the PAL machine versus 60Hz meant that the gameplay was generally a little slower on the PAL side?

The CPU clock is derived from the main clock for the VIC chip. PAL crystal is 8.867 MHz or alternative 4.436 Mhz (divided by 8 or 4 gives 1.108 MHz for the 6502). NTSC is 14.31818 MHz and after division results in a 1.02 MHz clock for the CPU.

[Mike]

I thought the 50Hz update rate of the PAL machine versus 60Hz meant that the gameplay was generally a little slower on the PAL side?

That is the case only for programs, which have their screen updates tightly coupled to a VIA interrupt synced to a raster line (like in the newer versions of rhurst's Quikman). The game "speed" could still be governed by yet another timer, moving the position of objects with sub-pixel accuracy, independent of PAL or NTSC.

Apart from that, a PAL VIC-20 is *faster* than an NTSC VIC-20, 1.10 MHz vs. 1.03 MHz. Programs which are not coupled to the vertical sync thus will generally run faster on PAL machines.

I was just thinking that the PAL screen had the capability to go higher res.

The pixels remain the same size, and since a PAL VIC chip can show more pixels than the NTSC VIC, that means the standard screen size shows more of the border.

Does the VIC display not have borders in NTSC land then?

There's still the border, in the 8 possible colours, but it is much smaller. Maybe less than 10% of the visible area on screen.

Different Kernel ROM. PAL has 901486-07, NTSC has -06 version. (the differences are mainly in default screen positions and some timing changes to make the serial port compatible with 50Hz or 60Hz timing)

- different default values for the VIC screen position registers, correct,
- different sets of timer interval values for the standard RS232 baud rates, and
- a different value for the jiffy timer interval value to obtain a 60 Hz clock - on both PAL and NTSC! - mainly because the clock speed of the CPU is different.

But there is no compensation for the different frame rates of PAL and NTSC, especially not regarding the serial bus (did you mean the baud rate table instead?)

[16KVIC20]

I must admit, I always did think the border was rather excessive in size. Some programmers seemed to circumvent those restrictions though.

[Mayhem]

If you've used Vice in both modes... the display area is the same resolution, the borders are bigger in PAL land.

[Mike]

Some programmers seemed to circumvent those restrictions though.

Yes, it is mainly the BASIC screen editor being 'hardwired' to a layout of 22 columns and 23 rows.

It needs just 4 register changes in the VIC to resize and reposition the screen window. MINIGRAFIK, for example, uses a screen window which corresponds to 20 columns and 24 rows. That can still be shown without problems on both PAL and NTSC. MG uses that window size, because it provides the highest number of pixels (160x192 = 30720), which can be bitmapped with the memory of $1000 to $1FFF without clobbering the lower 1K (system data), or using interrupts, on a standard VIC-20.

There are several games with character-based graphics (no bitmap), which resize the PAL screen window to something along 24 .. 26 columns and 30 .. 32 rows. 26x32 characters, or 208x256 pixels is about the maximum visible size on most PAL monitors which does just not crop the corners.

Since the standard screen window dimensions display only 176x184=32384 pixels, this is only 61% of the maximum visible area (208x256=53248 pixels) of a PAL VIC-20. The rest is border.

[SparkyNZ]

Sorry folks.. getting back to using 12VDC on the Vic.. Would a wall adapter delivering a max of 2.5Amps be sufficient? I'm wanting to ditch the PC PSU that I'm using and buy something smaller. (I'm actually attaching my Vic to a cable hanging out of the back of a PC which is a pain in the butt at the moment )

[Boray]

The fuse inside is 3A. But I measured once how much the Vic actually uses:
http://sleepingelephant.com/ipw-web/bul ... .php?t=308

"My vic-20 uses 1.64A while running and more like 1.75A at startup."

But if something goes wrong, I guess your PSU will take the damage instead of the vic fuse.

[SparkyNZ]

I bought myself one of those 12VDC 2.5Amp adapters. Its working great and staying cool!