Apple IIgs PAL video timing?

[bigmessowires]

Could anybody help provide some timing data for Apple IIgs PAL video, from the composite sync signal on pin 3 of the DB-15 monitor connector? This is probably the same as the timing from the composite video jack, but just in case it differs, I'm looking at the DB-15 monitor connector. I'm trying to understand how it might differ from NTSC, for the Mac Sync-inator.

On my IIgs, I've measured 15.7 kHz horizontal and 59.92 Hz vertical. For a IIgs that's built for a PAL region, would the horizontal rate stay the same and only the vertical rate would change to ~50 Hz? Or would the horizontal rate also change? I haven't been able to find a clear answer searching online.

 

[bigmessowires]

According to the standards for composite video, which Apple may not have followed exactly, NTSC should be 15.734 kHz horizontal and PAL should be 15.625 kHz. Reality may be different, as I'm measuring 15.70 kHz here rather than 15.734 kHz. So maybe Apple chose a single horizontal rate to split the difference between NTSC and PAL?

 

[bigmessowires]

I think I've got the Sync-inator working on the Apple IIgs, and the hsync/vsync output looks right on the logic analyzer, but none of my six LCD monitors are able to handle the 15.7 kHz horizontal refresh rate. If I had an appropriate monitor, I think it would work.

For the IIgs, this will draw comparisons to the Manila Gear Apple IIGS VGA Adapter. Without criticizing the quality product from Manila Gear, the Sync-inator takes a different approach and I think it may enable the IIgs to work with a larger selection of monitors (although 15 kHz capability is still required). The Manila Gear adapter uses the same approach as my first-generation prototype, with an LM1881 chip to extract a new vsync signal from the IIgs csync, but re-using the existing csync signal as an hsync substitute rather than creating a true hsync. When I tested this approach with higher resolution video from Macs, some monitors would accept csync as an hsync substitute, but some required a true hsync. So the second-generation Sync-inator was redesigned to allow for creating a true hsync.

Here's a look at what the Sync-inator is doing with my IIgs NTSC video:



The funny-looking signal at the top on VSYNC.in is because the IIgs puts composite video onto what's normally the vsync pin. The Sync-inator ignores this. CSYNC.in shows the csync signal from the IIgs for a few scan lines before and after the vertical blank. HSYNC.in from the IIgs does not have any signal. HSYNC.out and VSYNC.out shows what the Sync-inator is decoding and sending to the VGA monitor, and it's basically what you'd expect to see if the IIgs were designed to output separate horizontal and vertical sync signals.

If somebody has a IIgs and a 15 kHz capable monitor, I'd be willing to send you one of these for testing to confirm it works. Also if somebody has a PAL IIgs and a 15 kHz monitor, and an Atmel ICE or other AVR programmer that supports the ATTINY zero series microcontrollers, I'd be willing to send you one if you can help experiment with any firmware tweaks that may be needed for PAL. You will also need a serial cable and the ability to solder a couple of wires if you want to read the serial debug output:

* video reset
Big Mess o' Wires VGA Mac-Syncinator, firmware 1.0
sync mode: will be auto-selected based on the detected signal format
Detecting video signal format...
. video signal contains these sync signals: csync
. no activity was detected for these sync signals: hsync vsync
. csync horizontal period 63.7 us, frequency 15.6 kHz
. csync vertical period 16.6 ms, frequency 59.9 Hz
auto-select result: csync will be converted into separate hsync and vsync
running

 

[lisa2]

Hi Steve,
I am not sure there ever was a "PAL" version of the Apple 2gs, they were all NTSC ( apples variation of NTSC at least ).
I do have two apple 2gs systems and an apple 2gs RGB monitor for testing, if there is some way I can help, just PM me.
Rick

 

[NJRoadfan]

There was no PAL version of the IIgs, you an use the one you have. They all output NTSC composite video, only the power supply differs. The machine can be switched to 50Hz RGB output by pressing Press Option-Control-Reset and selecting option 3. In practice, nobody ran their machines at 50Hz output. Unlike other home computers, you will not get extra vertical lines of video and the CPU clock doesn't slow down.

I'm pretty sure the IIgs doesn't meet NTSC timings and specs. I have devices here that have trouble locking onto the color burst from the composite output. Heck, I have an Apple Video Overlay Card (yet another DB-15 RGB output device to test), a device that Apple claims meets RS-170a specs, and I have trouble getting color output from that! The IIgs also outputs slightly different dot clocks for 8-bit Apple II video modes and the SHR IIgs modes. This is enough to cause the AppleColorRGB monitor to lose horizontal hold if the h-position control isn't set just right.

 

[bigmessowires]

Ah, thanks for clearing up the PAL usage. I just tried it, and the Sync-inator seems to be working fine in Apple IIgs PAL mode. The horizontal refresh rate is unchanged at 15.7 kHz and only the vertical rate changes to 50 Hz. If I had the right kind of Samsung SyncMaster or other LCD with 15 kHz support, I think I'd get a picture. Until then, I'm using the logic analyzer to confirm the sync signals look correct.

 

[NJRoadfan]

Any concerns regarding the possible grounding of -5V depending on how the dip switches are set?

 

[Arbee]

I'm pretty sure the IIgs doesn't meet NTSC timings and specs. I have devices here that have trouble locking onto the color burst from the composite output. Heck, I have an Apple Video Overlay Card (yet another DB-15 RGB output device to test), a device that Apple claims meets RS-170a specs, and I have trouble getting color output from that!

That's surprising. The IIgs uses an off-the-shelf composite encoder chip, so it's the only Apple II that generates "true" composite color. I've never seen it fail on anything, from cheap VCRs to expensive LCDs.

 

[NJRoadfan]

The one notable device I had a problem with was the original RetroTINK 2X. No color at all, which surprised me as this device was built for computer generated video devices outputting at 240p. Same problem with the Samsung 940MP monitor that I have as a bench display.