Hello! As a part of restoring the CBM900 machine to life, I will need to provide adequate display for it. Since it has the hi-res card, a trivial MDA monitor will not work. Here's the info I gathered so far about the card: * The output has TTL levels for sync, but ECL levels for video data. This was presumably typical of high-resolution workstations of that era (Sun, Apollo etc). Actually the whole card is built with TTL chips, and TTL-to-ECL converter is placed just before the video signal goes to the connector. * Vertical refresh is 60 Hz (negative polarity), and horizontal refresh is 53.7 kHz (positive polarity). This means 895 scanlines, which makes the advertised resolution of 1024x800 very plausible. * The above parameters and resolution mean that the video clock would be somewhere around 64 MHz. A strange thing is that the card does not contain such oscillator (actually no oscillator at all) and I have no idea how that frequency would be derived from the system clock of 12 MHz (some kind of PLL?). * Surprisingly, there is no 8563 chip in the card. The whole card is built around TTL chips: http://imgur.com/kIgNsHi There are several 16V8 chips on sockets, and the big chip is a 82S105 PLA. There are no ASIC chip at all. Presumably this means that the card is simply a dumb framebuffer. * There is 128 kB of RAM on the card, which corresponds to the presumed 1024x800 mono resolution. The connector pinout in the documentation describes an "ECL+ Intensity" pin, but this is clearly an error as there is no corresponding "ECL- Intensity" pin, and additional intensity attribute would not fit in the supplied RAM. My idea is to build a simple converter to connect a multisync SVGA monitor. The obstacle I am currently facing is how to convert the video to VGA level. I would probably not bother in converting ECL back to TTL for that purpose, instead I will route the TTL vide to an unused pin in the connector. However I need a way to properly convert TTL levels of 0V/5V to VGA levels of 0V/1V. I am afraid that a simple resistor voltage reducer would be too slow to work in the 64 MHz range. This is an area where I have no expertise so I would appreciate some suggestions. Regards, Michau. Message was sent through the cbm-hackers mailing listReceived on 2014-07-24 09:00:03
Archive generated by hypermail 2.2.0.