EEPROM expansion (bank switch adapter)
A while back I created a set of little adapter boards to use as a way to expand the memory for the Parallax Propeller and also the OEM BASIC Stamp chips. A couple just had hard coded addresses for multiple EEPROM chips and worked out well. The one that was the most useful is the board replaces a single DIP EEPROM and will allow a pair of EEPROM chips to be installed instead and then bank switch between the two. It has a three pin header which is used to determine which chip is addressed at address 0 and which one at address 1. By moving a jumper (or connecting a SPST switch) you can toggle between the two chips. It just switches which chip is set to respond to address 0 or address 1.
This has been very useful for me since you can have two complete different images available and just swap them with the flip of a switch. I’ve use this on a small robot that was running an OEM Stamp so I could keep two entire programs loaded and just switch between the two without reloading the Stamp each time.
The adapter should work on most of the Propeller boards that are currently using a single DIP EEPROM chip for program storage. Boards like the DracBlade, PropRPM, PPDB (Propeller Professional Development Board), Briel PocketTerm, etc. It may work on the SpinStudio or Propeller Platform depending upon what other things you install on those boards due to physical interference.
Some boards like the Hydra and Hybrid Propeller boards already do some banking with the cartridge this adapter isn’t for those particular boards.
The board has two .1uf caps at the supply for each memory chip and two 10K pull-ups for the chip selection. It also has two open spots so you can add pull-up resistors (1206 package) on the SDA and SCL lines in case the board you are plugging the module into is missing them and you find that you need those resistors.
The spots for the two resistors on the SDA and SCL lines are optional. These are for the whole I2C bus not just one chip. If the micro has internal pull-ups enabled then you don’t need them. Most boards will already have whatever pull-ups are required so I would leave them open. They are in case you do need to add a pull-up resistor on the SDA or SCL lines. Some boards never had them and if you find that you do need them you can just add them on the adapter board. From what I have seen I think 4.7K or 10K is a value that a lot of people use (only if they need them).
When installing the 4-pin heads make sure the thicker lead gets soldered into the PCB. If you find that clearance is a problem you can use one (or more) regular 8-pin DIP sockets as extension for the height to help clear parts.
Attached is a picture of the adapter board itself, the adapter installed on a DracBlade board, and also one that shows the kit. The advantage of using it here is you can switch between a couple different emulators without reloading the EEPROM each time.
I have plenty of extra boards so I wanted to offer them here. Blank boards run $0.95 or the whole kit is $3.95 The kits include machine pin headers where it plugs into the socket so it doesn’t stretch out the contacts (like the square pins do) so you can easily go back to a single chip if you want. For those that may want a quantity of blank boards there would be a discount.
If you’d like one (or more) of these just send me an e-mail email@example.com with what you want (blank boards or kits) and location or zip code so I can get a total w/shipping.