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Rybags

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Everything posted by Rybags

  1. In theory you could, though generally SRam uses a different pinout and usually direct addressing rather than row/col so isn't an instant plug/play situation. Since SRam needs no refresh it would be possible to make an extra circuit that prevents the memory refresh cycles halting the CPU - some logic needed there since /Halt is also used for screen DMA and that has to remain in place (Antic provides /Ref which allows distinction between the 2 types)
  2. In theory if you could install only 32K then an XL would work with it in similar fashion to the old 400/800. The OS establishes a contiguous RAMSIZ value based on multiples of 4K so should work with any memory size 4K to 64K. 4K was the original specification for the 400 and of course would be a barely usable configuration - no Dos, any graphics mode needing over about 2.5K would fail and you'd be lucky to type in a program that took much more room than 1 screen worth of listing. The Acorn Electron I believe has 32K and is done so by combining 2 lots of 4 bit output from a 64k x 4 DRam on successive cycles to obtain a byte.
  3. I don't think 32k x 1 or x 4 bit chips actually exist. Generally DRam ICs have equal # of rows/columns which would give sizes: R/C Size 4 256 5 1024 6 4096 7 16384 8 65536 Though some 800 Ram boards used partially failed DRams which only used half their capacity, not sure how the R/C arrangement was set up there.
  4. Colour 3 is red on NTSC and PAL. Supposedly red also occupies 4 on NTSC but not on PAL (it's more towards violet) The problem of "pink" is due to lack of saturation. A8 colours are oversaturated in the 0-2 luma range, about right for 4-8 and undersaturated above that. Good idea for a mod there - saturation corrector though do the likes of Sophia allow modifying the palette?
  5. Thet's on Harmony cart so benefits from extra Ram, massive bankswitching and I believe the AVR processor which injects the 6502 code onto the bus to allow the greatly enhanced graphics and sound.
  6. Hum from the computer itself - not right. Maybe there's some AC coming through the power supply. Or maybe there's some sort of user modification that's playing up.
  7. Seems to be no dump of the firmware around. From a Hackaday page I got a link http://www.buildlog.net/blog/2019/10/inktober-project-2019-post-5/ It seems to do 3 stepper motor iterations for each pen change, so there's probably some slightly more complex operations on the parameter to obtain the result.
  8. Custom chips aside, most ICs and components are off the shelf and easily obtained. Given the youngest machines are now almost 30 years old, they've lasted pretty well. I bet if you recapped an XL just for the sake of it, they wouldn't last the same duration again.
  9. I'd guess it's only doing 8-bit maths operations. So worst case might be 255 times not that you'd want that. Ascii codes for 1 and - are 49 and 45, so potentially it could end up with a large number (assuming it's subtracting 48 from the parameter). How about if you use something like C; ? ; is Ascii 59 which would represent 10 rotations?
  10. 600/600 XL and the XEs all get their native voltage from the PSU. Any related damage is usually due to that rather than an internal failure. I might be wrong here but I don't think removing or having any internal cap fail would damage the computer at all.
  11. The best option IMO is something that causes minimal disturbance to what you're doing which would likely be typing in or modifying a Basic program. So, if it's creating new variables or inadvertantly trashing existing ones, not really good. The ones I did earlier - not the most speedy things and the immediate mode one gives the error 136. But minimalistic insofar as not using lots of variables and IOCBs.
  12. The brown cart metal cover isn't actually connected to the cart board in any way. Possible alternate purpose of the tab: - guide to assist insertion so the board lines up properly with the connector (esp 3rd party carts of the time without the interlock/door tabs. - ground attachment to assist dispersing static when inserting. - RF reduction means by joining the cart cover with the internal Faraday Cage.
  13. Have to wonder - how compact could an assembly version be made, like to sit near the bottom of Page 1. So then you could have something like ? USR(270) Or theoretically a stub could live in some free RAM down low with the directory program under the OS - done as an AUTORUN.SYS
  14. The problem using DIR.LST is you then need to put it on every disk you're likely to use. An alternate could be to just embed it in your current Basic program. Probably best to put it right near the end, and have it such that you can GOTO it in immediate mode and have it create minimal disturbance. So it might be something like: 32000 CLOSE #5 : OPEN #5,6,0,"D:*.*" : TRAP 32100 32010 GET #5,ZZ : PUT #16,ZZ : GOTO 32020 32100 CLOSE #5 : STOP STOP instead of END so that other IOCBs aren't closed and you can use GOTO to resume your program if you've hit Break somewhere.
  15. Too many Atari xyz? Is there such a thing? Probably. I'd have to say game controllers most likely. More joysticks than I'd be likely to use (at least 5), 2 or 3 sets of paddles though I think one is a C= set, Star Raiders 2600 keypads, a light gun (I think that's about the lot). But on the flipside there's lacking items too. Despite having about 11 A8 computers at my peak, I've only got 1 proper Atari RF cable, probably 2 others, and only 1 or 2 XL 5V power supplies.
  16. Fixed... the second 6 is only as it's ignored and easier to just repeat than do a 0.
  17. Standard scan mode is every 228 scanlines - they can return a value quicker but that's the maximum so should be assumed so. That's not far off the NTSC rate (262) - in theory you could do away with the OS routine and do your own that speeds it up to every 230 or so but hardly worth it. Fast Pot scan mode does it in 228 cycles (2 scanlines) which is somewhat quicker. The downside is that the accuracy will be somewhat less. If you can put up with the extra jitter then you could put them in fast scan mode and just leave the OS routine in place. If you only want a dozen or so readings per frame you could use DLIs which read the current POT value then start a new scan (POTGO). ALLPOT should be sampled first to ensure the previous reading is complete. From memory the Atari paddles operate on a resistance of 0-1M Ohms (Commodore uses 500K) - so you'd want your values spaced about evenly in that range. Low resistance should = lower POTn value since the voltage threshold of the caps is reached faster.
  18. Typing in a program can be an annoyance since it's interfering with what you're doing. A quick/dirty immediate mode method I used. If you've already used it recently then type END or CLOSE #1 first: O. #1,6,6,"D:*.*" : F. A=1 TO 9999 : GET #1,D : PUT #16,D : N. A It'll output the dir until error 136 occurs for EOF.
  19. Without other means it's theoretically possible to use an Atari tape drive to load a program to create a Dos disk. I think I might have created a rescue Dos maker years ago. Though it's not worth buying a tape drive just for the purpose since there's cheap SIO2PC types available.
  20. Supposedly the old NMOS is less prone to static damage then newer CMOS fab chips. You'd probably be fine just using a wire jumper with alligator clips to connect the ground plane on what you're working on to a ground nearby such as PC case, kitchen sink or (possibly) metal window frame.
  21. The PAL thing was just an aside, in the US I think all machines had the channel select. Likely as their VHF bands would have been more crowded than most places.
  22. Voltage? The switch just selects which channel gets the RF out. AFAIK no XL or XE for PAL has one, and I've looked at the 800 schematic. I'm fairly sure it just includes/excludes part of the RLC circuit with the end result of changing the offset of the final RF frequency.
  23. Like you said, multiply the indexes but the language has to do the same so the speed loss mightn't be so bad as you think.
  24. I get the feeling I've heard of this before. Maybe boot it holding Option? If the colours at the right are still present then the computer hasn't locked up as they're changed by the CPU.
  25. I was just about sure Ben Heck did a remake of his Atari portable computer which would fit the bill. Can't find it though. A 1080XEL might be makeable into a laptop though it'd probably be 3-4 inches thick.
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