Mac IIci + Griffin PnP 01 REV. A? How to get 640x480 or 512x384 ?

[MarcTremblay]

Hi all! Happy new year. I'm new to this forum. I just acquired a Macintosh IIci loaded with a copious 8MB of RAM. It only has onboard video and it didn't come with a monitor so I'm trying to hook it up to a 4:3 IBM ThinkVision (L171) using a Griffin PnP adapter (which both work great when hooked up to my PowerMac 7300 and PowerMac G4 MDD). All I can get with DIP switches set to 5,6,7 is squeezed portrait mode 640x870 in BLUE & BLACK (documentation says 5,6,7 is good for both 512x384 RGB *AND* 640x870 B&W portrait) https://www.pccables.com/pdf/MonitorAdapter_MacPnP.pdf

1) Does anybody know the correct DIP switches to turn on to get 640x480 or 512x384 for a Mac IIci? I don't mind if it's color or B&W, but I don't like the aspect ratio to be messed up

2) Does having perfectly stable blue & black 640x870 video from the Mac IIci on the ThinkVision mean that this monitor supports Sync on Green or is this unrelated?

I'd love to restore this 1980's beast!

 

[MarcTremblay]

I found the manual for my IBM ThinkVision L171 monitor: http://ps-2.kev009.com/pccbbs/options/l151ab6en.pdf#page=17

Those are its V/H frequencies:

• 30 - 63 kHz horizontal frequency
• 56 - 76 Hz vertical frequency

I suspect the issue is that the supported horizontal frequency range is just a tad too high on that monitor.

Apple's Macintosh IIci developer notes PDF is here: https://cdn.preterhuman.net/texts/computing/apple_hardware_devnotes/Mac IIci.pdf#page=56

According to it, the Mac IIci 640x870 resolution that I'm able to sync with my monitor is sent at a 57.2832 MHz horizontal frequency, while the 640x480 that I'm trying to get is sent at a much slower speed of 30.24 MHz. (Not sure those are MHz, probably they meant kHz?) Anyway, could it be that 30.24 MHz is just a bit too slow for that monitor?

Note: I've also found this, which might be interesting if I want to get myself a replacement LCD monitor that supports slower horizontal frequencies? http://15khz.wikidot.com

 

[MarcTremblay]

Alright, one more update. I have tried using another LCD monitor (Samsung SyncMaster 941bw). Lo and behold, it actually works, almost like magic! I've got 640x480 at 256 colors depth, no glitches, no refresh bars, smooth as silk.

In the manual online, I can see those supported frequencies:

• Horizontal 30 ~ 81 kHz
• Vertical 56 ~ 75 Hz

But there is even better, there's a table that explicitly talks about supported MAC timing modes and 640x480 is listed in there with those frequencies:

• Display Mode : MAC, 640 x 480
• Horizontal Frequency (kHz) : 35.000
• Vertical Frequency (Hz) : 66.667
• Pixel Clock (MHz) : 30.240

So basically, the 30.24 MHz that I had read earlier today was for "Pixel Clock". And it seems like that's what's different from the IBM ThinkVision monitor. So in a nutshell, although the IBM ThinkVision is older and in the correct 4:3 aspect ratio, does a worse job than the newer 16:9 Samsung SyncMaster monitor.

All is working with it, so I think I'll toss the old IBM monitor and just use the SyncMaster for all my old computing needs from now on!

Hope this helps someone. Have a nice day.