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Cartridge that takes a 28 PIN ROM


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Hi everyone,

 

I'm not very familiar with the Atari A8 offerings so I'm hoping for some guidance.

 

The project I'm working on requires a cartridge to plug into the back of my Atari 130XE. Is there a ROM cartridge that I can purchase with a 28 pin socket that will take a 16K or 32K ROM that I supply? Who would supply something like this?

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Default carts with no bank switching are a maximum of 16K, occupying memory from $8000-BFFF.  You can order 16K boards (27128 EEPROM compatible) from OSH Park - https://oshpark.com/shared_projects/YreZRvio

 

There are a number of different bank switching carts available, providing different maximum memories and footprints; some only occupy 8K of address space, freeing up more base RAM.

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The cartridge address space is 16K maximum and 8K minimum (you can have smaller Roms that'll usually give mirror copies in that 8K)

 

The maximum cartridge size is limited only by physical space constraints - with bank switching you can have access to a lot more data.

If you're doing experimental development then there's flash carts around such as from AtariMax http://www.atarimax.com

 

You might find them easier than flashing Eproms.  There's also a PC-based interface for flashing the cart images as well as the Atari based one which might be handy for a 6809 based system.

Some fudging around might be needed though, I'm not sure if the PC software tries to populate the home bank with the 6502 based menu program or allows to just flash in raw images.

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My plan is to write 6502 code for a proprietary serial-based protocol that I'm experimenting with. I don't know enough about the A8 ROM to understand what services are available. If I want to read/write data over the SIO, are there ROM routines for facilitating that at certain baud rates, or do I need to talk to the POKEY directly?

 

Also, I need some sort of serial cable from the SIO adapter to a DB9. I seem to remember there was something called SIO2PC that did that?

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I think you would do better to try writing your protocol for RS232 in the first place. SIO already has its own packet based protocol with support routines in the SIO bus driver built into the OS ROM. It is technically possible to write directly to hardware registers to send data over SIO but good luck with that !

 

If you had an 850 I/O module then you could program its RS232 ports to any of its supported speeds and then use its "R:" device driver to send it any data you like via the OS's Central I/O (CIO) system.

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The 2 main disadvantages of Pokey/SIO for serial you'll probably find - it uses start/stop bit and you have no choice in that matter.  Though you could use bit-banging techniques as an alternative (with the extra pain that would entail).  And it's 0/5 Volt levels, not RS232 which means interface hardware required for level conversion.

 

Advantages - since the audio circuitry dictates the bitrate it's pretty flexible in that sense though at the high end the steps get a bit big, but you won't necessarily be able to land exactly on a "standard" rate like 38,400 (but the hardware does allow some drift on input rate).

You can do poll driven I/O or interrupt driven.  In fact you can automate serial IO to the point where it's a near 100% background process and have a game going in the foreground (Seven Cities of Gold probably the best example of this)

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If you do SIO without using the /Command line then other devices will just ignore it.

If you wanted to implement your own protocol but use /Command it'd be easy enough to do so without disturbing other devices.

Then there's always the hybrid option of borrowing a joystick port and using it for control signals.

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  • 2 weeks later...

Hello everyone. I ordered several of these boards (https://oshpark.com/shared_projects/YreZRvio) from OSHPark and they came in today. I populated the boards, but am not able to bring up a ROM properly. I'm using a ROM emulator which I know works, and it's plugged into the 28 pin socket of the board. I added a 74LS00 to one of the boards and on another board I jumped pins 10 and 11 based on the instructions here (http://www.grandideastudio.com/wp-content/uploads/pp_atari8bit_instructions.pdf)

 

When I insert the cartridge into the back of the Atari 130XE and power it up, all I get is a black screen. Removing the cartridge and powering up the Atari 130XE shows the blue screen and READY prompt.

 

The cartridge can take both 8K and 16K ROMs, and I found a few online, downloaded the into the ROM emulator, and no go.

 

Is there a good "test" ROM image anyone can suggest to test out this cartridge so I can gain confidence that it works?

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The Atari OS has defined Central I/O routines (CIO) for standard methods of communicating with devices, which also permits redirection from one device to another.  So, for example, a routine could take input from a disk file instead of the keyboard by changing one argument.  Or output could go to the printer instead of the screen.  By going through CIO, you're guaranteed compatibility with different versions of the OS.

 

There's an into to CIO at https://www.atarimax.com/freenet/freenet_material/12.AtariLibrary/2.MiscellaneousTextFiles/showarticle.php?30 that may be of help.

 

 

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