Hello
I bought an Apple IIe PAL version with a 80col/64 k that has a very strange behavior:
Actually when in 80col mode, in text mode, one character out of two is drawn without its last pixel column.
in 40 col mode everything is ok, the problem only occurs in 80 col mode.
Actually, in 80 col mode, either in text or double hires, bits 5 and 6 (counting from 0) of main memory are handled on video as if they were replaced by bit 0 (counting from 0) of Aux memory!
Here are screenshots that illustrates the issue at http://zakor.dyndns.org:8095/appleII/videobug.zip
1.jpg is the aux video set to 1 : as you can see there is more than 1 pixel set! But 3 pixels
41.jpg is the aux video set to 41 (first and 7th bit set to 1): again the first bit is much larger than the 7th one (because there are here 3 pixels)
7F.jpg is the aux video set to 7F (all first 7 bits set to 1) with the whole main video set to 0: as you can see there is less free space for the main video bank!! As you can see on the TEXT below the graphics part, the right part of each second character (taken from the main memory) is truncated.
I discovered that in double hires mode the main memory video only uses the first 5 bits (instead of 7)For example, setting 2000:20 or 2000:40 makes no pixel appearing ! in normal hires mode everything is normal though!
Setting the AUX $2000 address to 1 makes appear three pixels on screen (as a wider pixel) AS IF main memory(to the left) has its 6th and 7th pixel set to 1. But if I read main memory in the monitor, it is still set to 0 !! (please refer to the 1.jpg screenshot). Besides there is NO left main memory to $2000 (since the first column is in AUX memory) and we have the same artifact.
So the problem seems to be a video signal problem, NOT a memory problem.
It seems to me that the video signal that is generated behaves as if bits 5 and 6 (counting from 0) of main memory were overwritten by bit 0 (counting form 0) of AUX memory. This should lead us to the faulty component I guess.
I also attached in the ZIP several files of a hires demo that shows the problem:
- ext80demo2.dsk disk image that contains a double hires program tests I used
- emulator.gif : the perfect result of the double hires 'cubes' test on the famous AppleWin emulator
- real.jpg: the result of this same test program on my apple IIe. As you see there IS a double hires problem
I hope to find someone who would be able to give me hints which component may be involved. Could you help me please?
Thanks a lot
cyril
I bought an Apple IIe PAL version with a 80col/64 k that has a very strange behavior:
Actually when in 80col mode, in text mode, one character out of two is drawn without its last pixel column.
in 40 col mode everything is ok, the problem only occurs in 80 col mode.
Actually, in 80 col mode, either in text or double hires, bits 5 and 6 (counting from 0) of main memory are handled on video as if they were replaced by bit 0 (counting from 0) of Aux memory!
Here are screenshots that illustrates the issue at http://zakor.dyndns.org:8095/appleII/videobug.zip
1.jpg is the aux video set to 1 : as you can see there is more than 1 pixel set! But 3 pixels
41.jpg is the aux video set to 41 (first and 7th bit set to 1): again the first bit is much larger than the 7th one (because there are here 3 pixels)
7F.jpg is the aux video set to 7F (all first 7 bits set to 1) with the whole main video set to 0: as you can see there is less free space for the main video bank!! As you can see on the TEXT below the graphics part, the right part of each second character (taken from the main memory) is truncated.
I discovered that in double hires mode the main memory video only uses the first 5 bits (instead of 7)For example, setting 2000:20 or 2000:40 makes no pixel appearing ! in normal hires mode everything is normal though!
Setting the AUX $2000 address to 1 makes appear three pixels on screen (as a wider pixel) AS IF main memory(to the left) has its 6th and 7th pixel set to 1. But if I read main memory in the monitor, it is still set to 0 !! (please refer to the 1.jpg screenshot). Besides there is NO left main memory to $2000 (since the first column is in AUX memory) and we have the same artifact.
So the problem seems to be a video signal problem, NOT a memory problem.
It seems to me that the video signal that is generated behaves as if bits 5 and 6 (counting from 0) of main memory were overwritten by bit 0 (counting form 0) of AUX memory. This should lead us to the faulty component I guess.
I also attached in the ZIP several files of a hires demo that shows the problem:
- ext80demo2.dsk disk image that contains a double hires program tests I used
- emulator.gif : the perfect result of the double hires 'cubes' test on the famous AppleWin emulator
- real.jpg: the result of this same test program on my apple IIe. As you see there IS a double hires problem
I hope to find someone who would be able to give me hints which component may be involved. Could you help me please?
Thanks a lot
cyril