Linards Ticmanis wrote: > I tried to get the Commodore 1084 Monitor to work with a Apple II > eroplus with pal card... it works fine in pure text or pure graphics > mode... however in mixed text/graphics mode the colors are messed up. I > wonder, does the 1084 maybe not support graphics lines and b/w lines in > the same frame? This is normal behaviour with any colour composite monitor on an Apple II. > The Apple does not produce a color burst in text mode, only in graphics > mode. In mixed mode the graphics lines do have a color burst while the > text lines don't. In mixed mode, the Apple II _does_ generate colour burst for the text lines. There is at least one exception: on an Apple IIgs with an RGB monitor, the VGC chip is able to switch to monochrome mode for the four lines of text. (It is actually fixed colour mode - on the IIgs, the user can set the foreground and background colours in text mode, and the border colour for all modes.) With a composite monitor and the text colours set to white on black, the IIgs behaves exactly the same as earlier models - you get green and violet for the text characters. -- David Empson dempson@actrix.gen.nz David Empson wrote: > In mixed mode, the Apple II _does_ generate colour burst for the text > lines. OK... probably true. However it seems that the PAL card that I use doesn't. It took me a while to find out that this card (made for a clone) expects an active-high TEXT instead of the Apple-provided active-low /TEXT on pin 23 of slot 7. So in an unmodified state I'd get colored text but B/W graphics. Exchanging one NPN transistor (2N3904), that shuts down the PAL quartz when active, with a PNP one (2N3906) that happened to be lying around fixed the problem - only in mixed mode I'd get the complementary colors (purple instead of green etc.) in a stripe covering about the second sixth of the screen, counting from the top, preceded and followed by a few lines in B/W. Also the text wasn't fringy, as it should be, derived from what you said. Only the top most line of text had a bit of a pinkish color to it. Totally removing the transistor gave color fringed text at all times, but with correct colors in the graphics. It seems that the /TEXT signal on pin 23 of slot 7 _is_ indeed pulled low for the four lines of text in mixed mode. Unfortunately I don't have an Oscilloscope, but a quick multimeter check showed a somewhat decreased mean voltage on the pin in mixed mode, compared to graphics-only mode. I guess either the quartz or the PAL chip TCA650 simply doesn't like to be switched on and off very quickly. I'll try inserting a 220uF capacitor between the transistor base and ground - combined with the base current limiting 4.7kOhm resistor that should delay the activation of the transistor for about 0.1s (if I calculated correctly), quite enough to get the quartz across those 4 lines of text alive. -- Linards Ticmanis The Master said, "The business of laying on the colors follows the preparation of the plain ground." Linards Ticmanis wrote: >I guess either the quartz or the PAL chip TCA650 simply doesn't like to >be switched on and off very quickly. I'll try inserting a 220uF >capacitor between the transistor base and ground - combined with the >base current limiting 4.7kOhm resistor that should delay the activation >of the transistor for about 0.1s (if I calculated correctly), quite >enough to get the quartz across those 4 lines of text alive. No crystal oscillator can be switched on quickly. That is the nature of a high Q circuit--it takes a while to settle down. Instead, the output of the constntly-running oscillator can be gated (ANDed with a control signal) very quickly, and this is the usual means of switching a clock signal on or off. Even if you can stabilize the color reference, it must b e supplied on each line--including during vertical blanking--so that the color monitor can maintain correct phase lock. This is another "high Q" circuit which must be kept supplied with a stable phase reference or color rendition will suffer--usually after just a few lines without a burst. This is why the Apple does not switch the color burst off during the text part of a mixed display--to do so would cause unspecified behavior of the the "color killer" circuit in the monitor, and poor rendition of the color for many lines after the burst was restored. -michael Email: mjmahon@aol.com Home page: http://members.aol.com/MJMahon/ Michael J. Mahon wrote: >>I guess either the quartz or the PAL chip TCA650 simply doesn't like to >>be switched on and off very quickly. I'll try inserting a 220uF >>capacitor between the transistor base and ground - combined with the >>base current limiting 4.7kOhm resistor that should delay the activation >>of the transistor for about 0.1s (if I calculated correctly), quite >>enough to get the quartz across those 4 lines of text alive. > > > No crystal oscillator can be switched on quickly. That is the nature > of a high Q circuit--it takes a while to settle down. OK, then my guess was basically right. > Instead, the output of the constntly-running oscillator can be gated > (ANDed with a control signal) very quickly, and this is the usual > means of switching a clock signal on or off. This is obviously not the solution in this case, because... > Even if you can stabilize the color reference, it must b e supplied > on each line--including during vertical blanking--so that the color > monitor can maintain correct phase lock. This is another "high Q" > circuit which must be kept supplied with a stable phase reference > or color rendition will suffer--usually after just a few lines without > a burst. And it did suffer. Quite badly in fact. > This is why the Apple does not switch the color burst off during > the text part of a mixed display--to do so would cause unspecified > behavior of the the "color killer" circuit in the monitor, and poor > rendition of the color for many lines after the burst was restored. Basically the circuit looks like this.... Quartz etc. Ground E C \ / \ / ===== PNP transistor 2N3906 B | --- | | 4.7kOhm resistor | | --- | | /TEXT from slot. I wonder what would be the easiest solution to delay the activation of the transistor? I thought about adding a someting like a capacitor (220uF maybe) in between B and Ground. The capacitor would be charged through the 4.7k in Graphics mode and then upon the switch into text mode it would slowly discharge through the resistor again. So both switching directions would have a delay introduced. The mean voltage in mixed mode should be high enough to keep the transistor inactive at all times then, so the quartz gets its working voltage and stays happy. Unfortunately my knowledge of electronics is limited, so I have no idea if this would cause my Apple to burn... -- Linards Ticmanis The Master said, "The business of laying on the colors follows the preparation of the plain ground."