xrbrevin Posted June 1, 2018 Share Posted June 1, 2018 Hi All, As per the title, I have struggled to find a guide for burning a standard OS ROM. I found a lot of resources for advanced ROM modding - ie multiple switchable ROMs on 1x chip etc but I just want to burn a replacement standard OS ROM. Does anyone know if it Is just down to which blank EPROM you use or are there some other mods required? much appreciated! Quote Link to comment Share on other sites More sharing options...
Rybags Posted June 1, 2018 Share Posted June 1, 2018 (edited) Standard 27128 EPROM is pin compatible with the XL OS slot and XE except XEGS. Generally OS images you find around the place will be exactly 16,384 bytes so no need to strip headers. The order is 4K that appears at $C000 then 2K Self Test at $5000 then 2K FP at $D800 then 8K at $E000. The MMU takes care of making things appear where they should, the programmer only need ensure the sections are placed in the right order. When doing modded OSes it's a good idea to calculate and store the checksums, incorrect checksum causes some software to not work. Some software refuses altogether to work with nonstandard OSes but in the modern day there's usually cracked versions available. Other threads around describe how to calculate the checksum. Also in modern times there's easier or alternate options like Ultimate 1 Meg or 32in1. Supposedly 32in1 can be flashed by placing it's chip into an 8 MBit Atarimax flashcart. Edited June 1, 2018 by Rybags Quote Link to comment Share on other sites More sharing options...
+Nezgar Posted June 1, 2018 Share Posted June 1, 2018 For a single OS, I beleive a standard 27C128 EPROM chip is a drop in replacement with no additional wiring needed on 600XL and 800XL. (And if your machine is socketed, no soldering either.) OS ROM on 65XE and 130XE are highly likely to be soldered to the board, and will require desoldering and socketing. XEGS uses a 32KB ROM (27C256) as it also combines BASIC and Missile Command into 1 chip. There's lots of OS ROM dumps around online, here is one place: http://ftp.pigwa.net/stuff/collections/atari_forever/ROM/ The 27C128 is 128 'Kilobits or 16 Kilobytes: 16x1024 = 16384 bits The TL866 EPROM programmer is a popular very cheap unit from China, many positive reviews of it here on AtariAge. It supports a very large number of EPROM types, and you get get other kits that include adapters for non-DIP type flash chips. I've used it to burn and read eproms as small as 27C32 (4KBytes) which are used in the 1050 OS. This one is $45 USD free shipping: https://www.ebay.com/itm/180926954184 If you don't want to go through the journey of acquiring burner and eproms, i'd be happy to burn for you for cost of postage and parts... Quote Link to comment Share on other sites More sharing options...
SoundGammon Posted June 1, 2018 Share Posted June 1, 2018 I burn 27128 chips on my ProBurner. They are 16K rom size is what a standard XL/XE uses. Quote Link to comment Share on other sites More sharing options...
SoundGammon Posted June 1, 2018 Share Posted June 1, 2018 I took the 400/800 OS (REV.A!) and added the Fast Math rom into my ProBurner and burned it to a 27128 chip and it works great in all XL-XE computers! Haven't tried it in a XE Game system. What's great about it is that basic, cart only, is faster with its math routines. And best of all, when you hit reset, it acts the same as turning the computer off and then back on again! Quote Link to comment Share on other sites More sharing options...
xrbrevin Posted June 1, 2018 Author Share Posted June 1, 2018 thanks all - i hoped there was a "drop-in replacement" time to dig out my TL866 and root out an EPROM - i saw an OS ROM image that reversed the way option works so i'll give that a go :) Quote Link to comment Share on other sites More sharing options...
JR> Posted June 1, 2018 Share Posted June 1, 2018 (edited) If you run any SIO devices capable of running at high speed...Happy 1050, sio2sd, sio2pc, etc., I would suggest looking into applying Hias' patches to a stock OS ROM. Pretty cool running sio2sd and sio2pc with POKEY divisor 0! A few other goodies in his patches too, like coldstart from the keyboard. It's what I run most often. http://www.horus.com/~hias/atari/#hipatch Edited June 1, 2018 by JR> 2 Quote Link to comment Share on other sites More sharing options...
xrbrevin Posted June 2, 2018 Author Share Posted June 2, 2018 sounds good, i'll give it a go! cheers Quote Link to comment Share on other sites More sharing options...
JR> Posted June 2, 2018 Share Posted June 2, 2018 There's one here with Hias + reverse option + fast math pack all ready to burn, with a correct checksum. http://atariage.com/forums/topic/206880-130xe-reverse-option-key-for-basic/page-2 3 Quote Link to comment Share on other sites More sharing options...
xrbrevin Posted June 21, 2018 Author Share Posted June 21, 2018 Hi, thanks for your help - ive made a single EPROM from a 27C128 with my TL866 but i also have an XE case with a hole already drilled in it the size of a chrome switch and im tempted to populate it!! can anyone advise if there is a way to use a 27C256 and a switch to have 2x OS ROMs available? Im sure i saw a guide somewhere but i cant for the life of me find it now. i think it said you pull a certain pin high or low to select the OS... thanks in advance! Quote Link to comment Share on other sites More sharing options...
ACML Posted June 21, 2018 Share Posted June 21, 2018 (edited) can anyone advise if there is a way to use a 27C256 and a switch to have 2x OS ROMs available? Yes, all you need is a single pole double throw (SPDT) switch. If I remember correctly, pin 27 on a 27256 would be the high bit select pin (two banks of 16K). You would burn the two OS on the 27256 and when you insert the EPROM in the OS slot, pull up pin 27 so it does not go into the socket. Then solder a wire from pin 27 of the 27256 to the center post of the SPDT switch. Then you need to connect the other two post on the SPDT switch (one to ground and one to +5VDC). The switch is now your OS selector switch and selects which 16K OS to use. Remember to only flip the switch with the power off. Edited June 21, 2018 by ACML 1 Quote Link to comment Share on other sites More sharing options...
xrbrevin Posted June 21, 2018 Author Share Posted June 21, 2018 hi, nice one, i'll set to work on it now i already know how to merge 2x ROM files into 1x 32k file so i think i have enough to do the job Quote Link to comment Share on other sites More sharing options...
+Nezgar Posted June 21, 2018 Share Posted June 21, 2018 I presume there's just 1 more pin and switch to switch between 4 OS's using a 27c512? This would be nice to replicate the stack of 4 chips in one of my machines with a single chip. Quote Link to comment Share on other sites More sharing options...
xrbrevin Posted June 21, 2018 Author Share Posted June 21, 2018 hmmm.. no joy with the 27C256, i can only get the 65xe to boot with the original (bad) OS ROM and sys-check II set to system test. it says the OS ROM is bad. i will root out a star raiders cart and see if that runs. do you know if there are jumpers to allow EPROM use - you know, like the 1200xl and 1050 have? Quote Link to comment Share on other sites More sharing options...
xrbrevin Posted June 21, 2018 Author Share Posted June 21, 2018 the EEPROM is an Atmel AT27C256R-70PU maybe it needs to be a slower ns model? Quote Link to comment Share on other sites More sharing options...
ACML Posted June 21, 2018 Share Posted June 21, 2018 I presume there's just 1 more pin and switch to switch between 4 OS's using a 27c512? This would be nice to replicate the stack of 4 chips in one of my machines with a single chip. You would need two SPDT switches. One would use pin 27 and the other I think uses pin 1. You would then wire the two separate SPDT like above. Pin 1 controls two 32K banks and pin 27 divides that into two 16K banks. I've done this with 27256, but not the 512. I've piggybacked two 256 to do what you want to do with a single 512. Quote Link to comment Share on other sites More sharing options...
ACML Posted June 21, 2018 Share Posted June 21, 2018 hmmm.. no joy with the 27C256, i can only get the 65xe to boot with the original (bad) OS ROM and sys-check II set to system test. it says the OS ROM is bad. i will root out a star raiders cart and see if that runs. do you know if there are jumpers to allow EPROM use - you know, like the 1200xl and 1050 have? I have found that some 1200XLs just don't like EPROMS. They give you a solid red or green screen, Have no clue why, but one out of every 6 machines won't boot using an EPROM. The 800XL may have a similar feature. Quote Link to comment Share on other sites More sharing options...
+DrVenkman Posted June 21, 2018 Share Posted June 21, 2018 (edited) I have found that some 1200XLs just don't like EPROMS. They give you a solid red or green screen, Have no clue why, but one out of every 6 machines won't boot using an EPROM. The 800XL may have a similar feature. Jumper settings on the motherboard? Remember, the motherboard jumper configuration on the 1200XL needs to be changed when converted from the usual 2 x 24-pin chip OS mask ROMs to a single-chip 28-pin ROM. Edited June 21, 2018 by DrVenkman 1 Quote Link to comment Share on other sites More sharing options...
ACML Posted June 22, 2018 Share Posted June 22, 2018 (edited) Jumper settings on the motherboard? Remember, the motherboard jumper configuration on the 1200XL needs to be changed when converted from the usual 2 x 24-pin chip OS mask ROMs to a single-chip 28-pin ROM. Copy that, but his application is not a 1200XL. It is a 600/800XL or XE. The W resistors on my 1200s are set for 28 pin packages, but I've found one out of six don't play well and won't boot from EPROMs. Same EPROMS in another 1200XL work just fine. Edited June 22, 2018 by ACML 1 Quote Link to comment Share on other sites More sharing options...
xrbrevin Posted June 22, 2018 Author Share Posted June 22, 2018 The 65xe i tried it in has other issues... i tried the above 27C256 in my 600xl and it works fine - thanks for your help! i then tried the 65xe stock OS ROM in the 600xl and it is also fine. None of the ROMs work in the 65xe - i can only get it to work when i plug in the sys check II so i will fit the switched EEPROM into the 130xe as originally intended - the switch will fill the hole nicely now i have a 65xe ROM reaing problem diagnostic on my hands!! any suggestions will be gratefully appreciated Quote Link to comment Share on other sites More sharing options...
+Nezgar Posted June 22, 2018 Share Posted June 22, 2018 What are your results with the 27C128 with just 1 OS in your various machines? Quote Link to comment Share on other sites More sharing options...
+Nezgar Posted June 22, 2018 Share Posted June 22, 2018 (edited) Would also be interesting to dump your problem stock ROM in 27c128 mode on the burner and compare with known ROM images to see if it checks out or is indeed bad reading that way too. Edited June 22, 2018 by Nezgar Quote Link to comment Share on other sites More sharing options...
xrbrevin Posted June 22, 2018 Author Share Posted June 22, 2018 hi thanks for your replies, the TMS27C128 now boots straight to self test and the second block is showing red. I'll give it an extra long dose of UV and try again because it did work before in the 600xl. none of the stock ROMs are defective (which is nice), my problem now is the 65xe has a fault when reading the OS and i get the trademark red/brown screen. I will do some continuity checks on the OS socket next - time to warp to jerzy sobola site (again) and warm up the mull-tim-etter... Quote Link to comment Share on other sites More sharing options...
+Nezgar Posted June 22, 2018 Share Posted June 22, 2018 (edited) If it's a dirty socket /bad contact in 65xe... sometimes an extra socket between helps when testing. Edited June 22, 2018 by Nezgar Quote Link to comment Share on other sites More sharing options...
xrbrevin Posted June 22, 2018 Author Share Posted June 22, 2018 never heard of that trick but alas it didnt alter anything all continuity checks ok with the OS socket - address and data buses, vcc, vss etc the MMU receives a line into pin 15 from the OS ROM pin 20 & 22 called "OS". next job is socket the MMU and swap it out Quote Link to comment Share on other sites More sharing options...
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