Note: This started out as a tech post here
Note 2: Thanks to ColinD mainly, he'd given me notes about a month ago when we saw this issue start up at the arcade but I was trying to understand what was happening.
Here we have one Atari System 2 Championship Sprint PCB with the following fault:
All the rest of the board is fine, the car sprites are doubling up the top 8 lines of them - displaying the full width no problem just repeating the top part.
After some poking around I was getting a bit lost, Colin chimed in with the help in the original tech post which resulted in me looking at the LS283 adder at 5M and 5L, both had what looked like signals going in and out - nothing obviously stuck.
Logic comparator was thrown on and immediately it disagreed with pins 9, 10 and 13.
Piggybacked a good 283 on the 5M and got this:
So we've got improvements. Pulled and replaced the 5M and now we have this:
So, another board lives.
The best I can understand of what's going on is that MOV0-8 going into 5M/5L are the vertical position of a given sprite, the 1V-256V is the current raster position.
These form an offset which via the pre-stored decoding in the PROM at 5P equates to adding and subtracting to get a data offset within the motion object ROMs
This happens for each line of the screen and where a sprite is within that raster line the current raster line taken from the sprites top line position is the offset plus the object number * 16 (16 lines per sprite) within the ROM is the final address for the current line to draw.
This data is then pushed into the motion object line buffers and offset using the shift controls via the 194's to put it at a definitive pixel X position along a line.
That line is then muxed with all the other stuff via the prioritising logic and ends up on the screen.
Yes, I only partly understand that so anyone who wants to explain the chain better please go right ahead as i'd love a better understanding of it.
Going back to my original post, the following I think are correct:
MOV0-8 are the vertical position of the given sprite.
MOPIC0-8 is the sprite number
MOSIZ0-2 are a sizing value but I don't think championship sprint uses these.
Anyway, thought i'd share the repair as a proper fix log so that its filed in the correct place. Those who follow me on YouTube etc expect a video to appear in the next day or two.
RGP2015-05-19 00:43:29
Note 2: Thanks to ColinD mainly, he'd given me notes about a month ago when we saw this issue start up at the arcade but I was trying to understand what was happening.
Here we have one Atari System 2 Championship Sprint PCB with the following fault:
All the rest of the board is fine, the car sprites are doubling up the top 8 lines of them - displaying the full width no problem just repeating the top part.
After some poking around I was getting a bit lost, Colin chimed in with the help in the original tech post which resulted in me looking at the LS283 adder at 5M and 5L, both had what looked like signals going in and out - nothing obviously stuck.
Logic comparator was thrown on and immediately it disagreed with pins 9, 10 and 13.
Piggybacked a good 283 on the 5M and got this:
So we've got improvements. Pulled and replaced the 5M and now we have this:
So, another board lives.
The best I can understand of what's going on is that MOV0-8 going into 5M/5L are the vertical position of a given sprite, the 1V-256V is the current raster position.
These form an offset which via the pre-stored decoding in the PROM at 5P equates to adding and subtracting to get a data offset within the motion object ROMs
This happens for each line of the screen and where a sprite is within that raster line the current raster line taken from the sprites top line position is the offset plus the object number * 16 (16 lines per sprite) within the ROM is the final address for the current line to draw.
This data is then pushed into the motion object line buffers and offset using the shift controls via the 194's to put it at a definitive pixel X position along a line.
That line is then muxed with all the other stuff via the prioritising logic and ends up on the screen.
Yes, I only partly understand that so anyone who wants to explain the chain better please go right ahead as i'd love a better understanding of it.
Going back to my original post, the following I think are correct:
MOV0-8 are the vertical position of the given sprite.
MOPIC0-8 is the sprite number
MOSIZ0-2 are a sizing value but I don't think championship sprint uses these.
Anyway, thought i'd share the repair as a proper fix log so that its filed in the correct place. Those who follow me on YouTube etc expect a video to appear in the next day or two.
RGP2015-05-19 00:43:29
