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Best way to disable a SARA chip?

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#1 Wickeycolumbus OFFLINE  


    Red Sea Crosser

  • 5,085 posts
  • Location:Michigan

Posted Sat May 7, 2011 12:27 PM

Not sure if this is the best place to put this topic...

I've been working on a code uploader for the 2600 that uploads code via parallel port to a special RAM cart. I built a RAM cart yesterday using a modified F4SC board from CPUWIZ and an HM628128 SRAM chip. I'd like to be able to enable and disable the SARA chip, giving me the option to test F4 or F4SC code.

I performed a modification to allow me to do just that, which worked perfectly with EPROMs. Once I tested it out with the SRAM chip however, code will not upload with the SARA chip disabled. Here is how I have everything hooked up:

628128       PCB connection

CS2          +5v
/WE          2600 R/W (connected via additional cable attached to cartridge)
/CS1         /CE

Then I have a DPDT switch hooked up like this (to select/deselect the SARA chip)

A12 input of bankswitching PLD
                                          o---------- EN_OUT from SARA chip 
                                          o---------- A12 from VCS

A12 input of SARA chip
                                          o---------- A12 from VCS
                                          o---------- GND

As I've said, SARA gets selected/deselected fine with EPROMs. Code uploades fine with the SARA selected, but for some reason will not upload with SARA disabled. Anyone know what the problem might be? Thanks!

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