8k and 16k carts question

[xrbrevin]

i have a few pixels-past PCBs so i wondered if they would work with any 8k or 16k ROM/BIN file?

i am aware that ROM files over 16k have their limitations due to the various bank-switching schemes but am i right in thinking this does not apply to the 16k or less files?

 

my understanding of cart operations is limited, can anyone recommend a simplified read on the basics?

cheers!

 

http://www.grandideastudio.com/pixels-past/

[+Nezgar]

Generally "Yes" - if its a straight up classic 8KB or 16KB ROM dump (remove CAR header so its exactly 8192 or 16384 bytes) it should work.

 

Looking at that PCB, 8K or 16K mode is determined by the presence or lack of a 74LS00 at U2. ie - 8K game doesn't need the logic chip.

 

so yeah.. just burn an 8K game to a 27c64 EPROM, or a 16K game to a 27c128 EPROM and it should just work!

 

An 8K game would probably work with a PCB configured for 16K in a pinch, but you'd lose 8K of RAM that would be useful for programming languages, ie BASIC or Assembler/Editor.

 

I haven't used these PCB's, but they look like a nice alternative to the genune atari EPROM cart PCB's from the likes of B&C or BEST, as they claim to fit in Atari brown cart shells.

[Rybags]

Note that there actually are some 16K carts such as OSS languages that are banked & sit within the upper 8K space only.  The addres space a cart occupies is determined by the RD4 & RD5 inputs.

[xrbrevin]

thanks for the further info.

i have dragged all my 8k & 16k ROM files into "the!cart studio" and in the content type column many are shown as "unknown" or "5200 one/two chip".

i suppose i can use a socket on the cart PCB and try a few out to see if they boot up.

 

i read some time ago (cloudy memory...!) that on bootup, (up to) 16k from the cart is copied to the Atari RAM and the computer runs the software from RAM. carts over 16k require the bank-switching process so in theory any 16k ROM file should be happy to boot. - except for OSS carts Rybags mentioned.

i'll have a look through the atarimania library for more info but if anyone can recommend a good read on the subject i'd be v.grateful

cheers!

[+Nezgar]

Definitely use a socket, regardless. Best is a machine / round pin / turned socket type socket. If you plan on experimenting a lot, you could try an EEPROM which has instant erase in a PC based programmer instead of waiting for the traditional UV light bake time... ATmel 28c64 and 28256's seem common on ebay, not 28c128. With a xx256, you can just repeat the 8K 4x or 16K 2x to fill the 32K space.

 

8K and 16K carts generally to not copy themselves to RAM. they basically replace 8K or 16K of the RAM in the computer with ROM. ie - a 48K 800 computer with an 8K cart present (like BASIC) only has 40K of usable RAM. With a 16K cart present, only 32K or ram is usable. They replace memory at the 'top' of the normal 48K RAM in the memory map, ie the memory from 40K to 48K for 8K, or 32K to 48K for 16K. a 32K Atari 800 is the same as a 48K Atari 800 if a 16K cartridge is present.

 

These simple carts have no way of 'disabling' themselves to get that memory back. Any writes to the 16K or 8K cartridge space will do nothing with the respective cartridge present - hence why some cartridge 'copy protection' techniques included writes to those memory locations, as it would trash the game code otherwise.

 

Later carts like XEGS bank switching cartridges could do tricks to 'load to RAM' from the cartridge (kind of like an emulated disk drive) and then turn off completely (via a special register) to regain all of the RAM that the cartridge would otherwise block access to.

[Rybags]

Copying to Ram is a dubious way to attempt to run a cart - in the case of the normal legacy Atarimax flash cart that has to be done for 16K games as the Rom only maps to the top 8K.

The "dubious" definition being that the bulk of games programmed knew of cartridge copying so overwrote some Rom addresses as a copy protection method.

 

That said though, the vast majority of such games were cracked a long time ago.

Edited August 11, 2019 by Rybags

[+DrVenkman]

8 hours ago, Rybags said:

Note that there actually are some 16K carts such as OSS languages that are banked & sit within the upper 8K space only.  The addres space a cart occupies is determined by the RD4 & RD5 inputs.

Just an FYI if anyone wants to burn one, there’s a 16K linear .CAR version of Action! that got put together in the last couple of years. It can be found in the 8-bit Programming forum and the Atari Wiki website. 

[Gunstar]

14 minutes ago, DrVenkman said:

Just an FYI if anyone wants to burn one, there’s a 16K linear .CAR version of Action! that got put together in the last couple of years. It can be found in the 8-bit Programming forum and the Atari Wiki website. 

Cool, I'll check it out. Though I'm not sure if it will be of use to me on my 1200 with MyIDE 2, since I have Mr. Atari's MyIDE 2 hacked OSS roms which, so far, work spectacularly with MyIDE 2 & SpartaDOS X cartridge piggy-backed as well as with MyBIOS/MyDOS. And @flashjazzcat recently had someone else (I forget who) make versions to work with SiDE 2. 

[+DrVenkman]

3 minutes ago, Gunstar said:

And @flashjazzcat recently had someone else (I forget who) make versions to work with SiDE 2. 

That was done in conjunction with @ebiguy. Which reminds me, I still need to flash my SIDE2 (and the U1MB boards inside my 1200XL, 1088XEL and 1088XLD). Sounds like a good task for today!

[+David_P]

For those interested, the Pixels Past boards are available to order from OSH Park.

[Wrathchild]

2 titles I converted to work from a 16K cart in 16K of RAM

RainbowWalker.rom JetBootJack.rom

[xrbrevin]

1 hour ago, David_P said:

For those interested, the Pixels Past boards are available to order from OSH Park.

ive just tried: www.jlcpcb.com

the first order discount is v.impressive and the manufacture time is swift but the item is in transit at the mo so i cannot comment on the results at this time

[BillC]

On 8/10/2019 at 2:44 PM, Nezgar said:

An 8K game would probably work with a PCB configured for 16K in a pinch, but you'd lose 8K of RAM that would be useful for programming languages, ie BASIC or Assembler/Editor.

All that's required to use a 16K PCB as an 8K is to cut the trace which connects RD4 to +5V, details about this are available in the following thread.