On 08/12/2011 12:10 AM, Hársfalvi Levente wrote: > Hi!, > > > On 2011-08-11 18:32, Gerrit Heitsch wrote: >> >> So I noticed when I tried it yesterday evening... Oh well, another >> pretty theory shot to hell... >> >> The reason I came up with this idea was that I read a posting on this >> list where someone stated that the 6510 and the 8500 have the full 8 bit >> port on die and that you could use some clever coding to distinguish >> between a 6510 and an 8500. Go look for the thread called '6510 and 8500 >> differences'. > > Ah, Nicolas Welte's findings about the unimplemented portbits of the > 6510/8500 (...one kind of stuff I like cbm-hackers for :-) ). > > Thinking it over, even that one seem to contradict with the idea of a > full 8-bit port that was supposed to be implemented on the 6510/8500's > die. Bits of the output register don't fade out by the corresponding I/O > pins absence. They do if you think of the circuit between the output driver and the pad and the pad itself as being the same as a capacitor of a DRAM cell. Once charged by the output driver, the charge will slowly dissipate. The speed depends on the process of the circuit, the temperature of the chip and the chip itself (production variations). > ...Hmmm, as I can see, visual6502.org don't list either the 6510, or the > 8500 (...and not even the 8502) in their collection yet. I got an email that my 8501 was received and it's also not listed yet. Since these people do this in their spare time, I don't mind waiting until they get around to it. >> The 6529B is an odd chip, no reset, no PHI2, no DDR... And I've only >> seen it in the 264 series and I've never head about one going bad. >> Replacing it with TTL chips would still need a handful though. > > Definitely. The single broken one that I have (and ever encountered) > just died because of some Chuck Norris descendant who seem to have > removed most chips from this Plus/4 motherboard, and put them back by, > err, applying some force. So that a couple of pins of the chips just > broke off / some broke out of the packaging :-/. If the pins are just broken off, you can usually fix them by removing a bit of the expoxy, then solder a piece of wire to the exposed part of the lead frame and then plug the whole thing into a socket and from then on treat IC and socket as a unit (I also use the socket idea with desoldered ICs). If the pins got removed completly, you're out of luck though, soldering something to the bonding wire is something I would only attempt if the IC in question is truly irreplaceble. >> There is one thing I have to do soon, find out why the video output of >> all C16 I have seen so far contains enough chroma signal on the luma >> signal that most monitors will only need the luma signal for a color >> image. Could be the routing of the traces between TED and modulator or >> the modulator itself that's 'leaking' since it's the part that produces >> the composite signal. > > That's the RF modulator. The luma signal doesn't look contaminated until > it enters the RF modulator (checked with an o'scope). And it looks > terrible, right after it exits. So I suppose it's the RF modulator. > > It's interesting to note that the RF modulator used in the 264 series > differs from those in any C64 motherboard versions. Probably cheaper... The PAL modulator also has a little switch inside that I never was able to find out what it's good for. >> I have a little cicuit (from a german forum for >> the C64) that allows you to remove the modulator in a C64 and still have >> S-Video output. The picture looks much better but you no longer have >> composite video, only S-Video. This should also work with TED, the >> output drivers on the chip seem to be the same as in the VIC-II. The >> circuit is just a 1N4148, 2 transistors BC547 plus a few resistors and >> 2 capacitors. > > Yeah, if you replace circuitry that interfaces the thing to the outside > world (ie. video signal buffers) that should greatly help. > > Fixing the rf modulator (learning how ie. the one found in late C64s > work and modifying the Plus/4 modulator accordingly) might be another > option. ...Possibly, it just won't worth the effort. Yes... unless it's a collectors item like a real 232, I see no reason to have an RF modulator anymore. All TVs have at least composite input and most have S-Video. Since it's easy to create composite from S-Video (a single capacitor, can be put into a DIN plug) I see no reason to keep the modulator in place, especially in the C16 that gets used most often. Gerrit Message was sent through the cbm-hackers mailing listReceived on 2011-08-13 16:00:03
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