Atarisrule Posted March 8, 2015 Share Posted March 8, 2015 I'm working on some 800's and thought I had one all buttoned up, but on the final check I found it was not loading disks all the way to DOS. It will load to Basic then load DOS but stops (locked up) every time at "Disk Operating Sys" on the top line. This is consistent on every regular DOS disk and on three drives, an 810, 1050 and IndusGT. I loaded OS/A+ to see what happens and it loads to D1: no problem but when entering DIR sometimes it completes the task and other times maybe one or half of the files list before lockup. These same disks and drives work just fine on another 800 using the same OS board. I can swap parts to see what's wrong but I hope someone has an idea which component could be causing this. It seems to forget to ask for all the info from the drive or locks up before finishing. The "boop" sounds just stop. Note I did try each of the RAM modules independently and there was no change in the random directory behavior or consistent DOS behavior. Also with no Basic cartridge and loading straight to DOS it also stops at "Disk Operating Sys". This must be one sector of data and it fails to ask for more. CPU? ANTIC? GTIA? POKEY? Other? Quote Link to comment Share on other sites More sharing options...
+Stephen Posted March 8, 2015 Share Posted March 8, 2015 My initial guess would be Pokey. Quote Link to comment Share on other sites More sharing options...
Paul Westphal Posted March 8, 2015 Share Posted March 8, 2015 My first guess is the o.s. Chip. Could also be antic. Swap Rom boards, and see what happens. Cpu might also have trouble with higher functions, but doubtful. Quote Link to comment Share on other sites More sharing options...
Atarisrule Posted March 8, 2015 Author Share Posted March 8, 2015 Thanks for the replies. The problem did NOT follow the ROM board. I used the same ROM boad when I tried it on the other computer that did not exhibit the fault. I thought it might be the POKEY also since it controls I/O, but on the Atari there are no on-board drive controllers so I have my doubts. I'll have to swap the CPU board today and see what happens. If that doesn't do it I'll try the Pokey chip. Quote Link to comment Share on other sites More sharing options...
Paul Westphal Posted March 8, 2015 Share Posted March 8, 2015 Yeah, Steve is right. Pokey. Quote Link to comment Share on other sites More sharing options...
Kyle22 Posted March 8, 2015 Share Posted March 8, 2015 The PIA is also involved in SIO. Quote Link to comment Share on other sites More sharing options...
Atarisrule Posted March 8, 2015 Author Share Posted March 8, 2015 I swapped the CPU board and it seems to have fixed it. Lots of programs that would not load or glitched are now functioning normally. I'm not sure which of the three is bad but a replacement assembled board should not be hard to find. Quote Link to comment Share on other sites More sharing options...
Kyle22 Posted March 9, 2015 Share Posted March 9, 2015 Here's B&C's listing on ebay for a complete replacement CPU board (the good one). You can use a 65c802 on it as-is, or a 65c816 with the addition of 1 jumper wire. http://www.ebay.com/itm/Atari-400-800-CPU-6502-PCB-Tested-Working-with-GTIA-/130887512770?pt=LH_DefaultDomain_0&hash=item1e7980f2c2 Quote Link to comment Share on other sites More sharing options...
Atarisrule Posted March 9, 2015 Author Share Posted March 9, 2015 I saw that ad earlier. I assume it has a Synertek 6502B on it. What is the 65C802 and why would I use it instead? I'm sure this has been widely discussed so maybe you could point me to a thread summarize here? Note that my good CPU board has a 6502A and the bad has a MOS C01437705. Quote Link to comment Share on other sites More sharing options...
Kyle22 Posted March 9, 2015 Share Posted March 9, 2015 The 65c802 is instruction compatible, and pin compatible with the 6502, and is also instruction compatible with the 816. The 65c816 is a little different, but will work with 1 jumper on the CPU board of the 800. Now, know that the 65c802 is pin compatible, but it CANNOT address the upper RAM. It is limited to 64K, just like the original 6502, but it has the "extra" instructions of the 816. The 65c816 allows 24 address lines, instead of 16. It supports 16M of RAM. This involves multiplexing of the Address and Data lines, and requires a memory expansion card that understands the addressing mode. These memory cards must be capable of understanding the multiplexed address and data lines. As far as I know, (as of now), there are not any extended memory cards for the 800 that support 816 high RAM. I wish there was one Quote Link to comment Share on other sites More sharing options...
Atarisrule Posted March 9, 2015 Author Share Posted March 9, 2015 Okay, so it can do more. However in my otherwise unmodified 800 is there at benefit? Processng speed or 64K (vs. 48K currently)? I do have an open memory slot (one board is 32k) but to my knowledge the system will not recognize anything over 48K. If it's an easy mod I might consider it. Quote Link to comment Share on other sites More sharing options...
Kyle22 Posted March 9, 2015 Share Posted March 9, 2015 (edited) I have the 802 and the Incognito in mine. I'm waiting for someone to make a nice RAM card for the 816. http://atariage.com/forums/topic/206900-incognito-production-installation/?hl=%20incognito It gives you XL/XE compatibility, Internal SpartsDOS-X, hard drive, multiple BASICs, multiple OS ROMs. This is a "Can't live without" piece of hardware Edited March 9, 2015 by Kyle22 Quote Link to comment Share on other sites More sharing options...
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