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