Andrew I’ll try and help out. Please put me down for 2 boards. John From: n8vem...@googlegroups.com [mailto:n8vem...@googlegroups.com] On Behalf Of Andrew Lynch Hi Leon! Thanks! Not to my knowledge. There were only a few prototype boards made. Your efforts are making the S-100 VDP project possible! The VGA interface is highly experimental. We got something akin to it working on the ECB ColorVDU board in converting RGBi to VGA. Most VGA monitors, especially CRTs, will not be able to sync to the lower scan frequencies. However many of the newer LCD monitors share circuitry with modern LCD TVs and can sync at NTSC scan rates or even perform scan rate conversion by default. It is a neat trick not too many people know about. It does work though! http://n8vem-sbc.pbworks.com/w/browse/#view=ViewFolder¶m=ECB%20COLOR%20VDU
From: n8vem...@googlegroups.com [mailto:n8vem...@googlegroups.com] On Behalf Of Elsid Hi Andrew, Sure, I can check things look OK on the new board design. I don't think I ever got the VGA output going. Did anyone else have any success with this board? Best regards Leon Hi Leon and Pontus! Thanks! Remember the S-100 VDP project? I’ve finally found some time to update the circuit to include the AY-3-8910 sound generator, VGA monitor interface, and do some other clean ups. Would you please check out the schematic and PCB layout and compare against your notes from the last prototype build and test? I would like to do another round of the S-100 VDP prototype boards and would like to make sure all the lessons we learned from the first prototype are fixed. Thanks and have a nice day! From: n8ve...@googlegroups.com [mailto:n8ve...@googlegroups.com] On Behalf Of Elsid Hi Andrew, The additional caps across the V9938 power pins are an attempt to make the video less noisy. They didn’t seem to have much effect. I suspect the noise I’m seeing on the video signal on the CRO may be due to the routing of the power lines for the video amp through the dynamic RAM circuit. (lots of hash from the refresh?) Maybe the video output could be routed away from the RAM and separate traces for the video amp power from the regulator provided. The extra pull up on DHCLK p3 of the V9938 (and cut trace to R53) is there because I was worried that the 5.37MHz output would be doing something to the LightPen inputs LPS and LPD. The 470 ohm pull downs on R, G and B outputs (p22, p23 and p24) on the V9938 are there because I suspected I may have damaged the COMP_VIDEO output (p21) and needed the pull downs to get the internal transistors to drive – the output was OK as it turned out. The reset circuit needs some changes. The V9938 is not receiving a “power on” reset because BRD-RESET* is being gated by SYNTMS* at U27C. (SYNTMS* is reset at turn on by BRD-RESET*). The V9938 has to the manually reset by toggling SYNTMS*. I have tried the FMS6141 video amp configuration and it works fine. Parts of the board working/not working: 1. Address decoding – working but could do with changes to make more MSX compatible – as you’ve said. 2. Reset circuit – only working manually – see comment above. 3. Composite video output – working but noisy – power routing? 4. Video RAM – working – I tried adding in 100 ohm resistor in the RAS,CAS and R/W* lines (like some MSX2 designs I’d seen) to reduce ringing. It didn’t reduce the video noise but it may be a good idea anyway. 5. BT478 – I haven’t tried yet but maybe we can route the RED, GRE and BLU outputs to a header for a DBS15 connector to drive a 15kHz VGA monitor. Best regards Leon Byles
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