32k Flash Cart Rev. 2

[cschell]

Incorrect, the 16F877 runs at 20Mhz, even the 16F84 can be clocked at 10Mhz. Some of the newer ones go even higher.    

 

No, I'm right. Yes, you clock it at 20 MHz, but PICs execute on instruction per four clock cycles. So it really only runs at 5 MHz. 200 ns per instruction.

 

Chad

[Cupcakus]

Cupcakus:

 

Do you really have F8/F6/F4 working?  The parts you pointed out on your board don't seem to possess any sort of comparator to implement even F8.  Are you just not pointing out other parts hidden under the wires, are does the bankswitching work only in theory?

 

You also realize that to do Superchip games you'll need SRAM on the board as your eeprom is almost certainly not fast enough to serve that purpose, right?   It also greatly complicates the deglitching required.

 

I installed the PLD shortly after I took those photos... I'll take more with the PLD in place... I really do have those switching scheme's working...

 

I do also realise that i will need an extra RAM chip... it's right here on my desk :-) and I have no doubts that implementing it won't be extremely frustrating.... The EEPROM is not only not fast enough, but as Eckhard pointed out, the EEPROM's life is around 100,000 writes or so... and using it as RAM would pretty much destroy it...

 

 

Everyone:

 

Sigh.  As I suddenly find myself with free time, the temptation to put out another run of Cuttle Carts grows.  

 

Chad

 

 

NOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO!!!!!!!

 

Man that would suck!! :-)

[CPUWIZ]

Incorrect, the 16F877 runs at 20Mhz, even the 16F84 can be clocked at 10Mhz. Some of the newer ones go even higher.    

 

No, I'm right. Yes, you clock it at 20 MHz, but PICs execute on instruction per four clock cycles. So it really only runs at 5 MHz. 200 ns per instruction.

 

Chad

 

You are absolutely correct, I misread what you were saying, I was thrown off by how you worded it. One instruction takes 1 cycle (well 2 for branches) which occupy 4 oscillator periods. Same thing, different words, I apologize.

[Richard H.]

I don't think PICs are fast enough to do Atari bankswitching. They run at only 5MHz max, which leaves less than 5 instructions per Atari clock cycle. Given that a jump command takes 2 instruction cycles on a PIC, that means that your loop could only have three instructions and still execute every 2600 cycle. The PIC is 8 bit, so you need to compare the inputs on two ports to detect a bankswitch address. Just reading both ports is two cycles minimum. Uh oh....  

 

Ahh.....yes...that would explain the glitches I've been experiencing.

 

SH*T ! - I did suspect it was that

 

Looks like I'm out of the race untill I find something more powerful

 

 

How does your RAM cart work... how do you program it???

 

The SRAM is fully connected to the MC's ports. A byte received by the PIC from the PC and placed on the SR's data port. It's then written by controlling the WE, and the Addr port incremented ready for next byte etc - it's very simple in practice.

 

It's also got a rock solid verify, as the SR is read after the write, and sent back to the PC.

 

How much memory is on it?

 

64K (32K on VecRAM) + on a 877 there's plenty of free ports to go much higher.

 

Is it nonvolatile?

 

It uses SRAM, but could use FLASH / EEPROM just as easily.

 

What bankswitching schemes do you plan to use

 

I was planning on putting them all in, but it's turning out to be more complicated than I had at first imagined

 

 

 

Hey ! - the fun part is the experimenting bit right ?

 

 

 

Richard H.

[Rob Mitchell]

As I suddenly find myself with free time, the temptation to put out another run of Cuttle Carts grows.    

 

Yeah .. especially with someone making $200 profit on the resale of one.

 

Will I be able to get a serial port version? ..... please?

 

Rob Mitchell, Atlanta, GA

[Richard H.]

Will I be able to get a serial port version? ..... please?  

 

 

Rob, I can make you a 2K/4K Atari adaptor to use on the VecRAM for the time being, if you want ?

 

 

 

 

Richard H.