Expanding number of variables?

John Mac

Is it possible to add RAM (or whatever it takes) to allow an increased number of variables on a BS2? With only 32 bytes (some of which are used for special registers), that leaves no room for arrays of any significant size.

Mike Green

There's no way to expand the variable storage area of any Stamp. The scratchpad RAM available in different sizes in most Stamp models other than the BS2 is often used for array type access. There are special statements (GET and PUT) used that work like an array that are used to access this area.

You can add external memory like EEPROM or Ramtron's FRAM as I/O devices. There are some serial RAMs that use the SPI protocol that only require 3 I/O pins for access and work with the SHIFTIN / SHIFTOUT statements like any SPI device. Some of the real time clocks (RTCs) have battery backed RAM. A BS2 doesn't have built-in statements for things like EEPROM or FRAM or RTCs, but the other Stamp modules have the I2CIN and I2COUT statements which make it really easy to use these devices.

If you really must have more RAM, you should consider the Propeller which has plenty.

John Mac

OK Thanks

26 bytes is awful limiting...so it's either a Propeller as you suggest or go entirely to PIC Micros.

Mike Green

You could also use an SX using SX/B for programming. The SX has more memory than the Stamps, about 250 bytes. Most of the Stamp models (other than the BS1 and BS2) use an SX for their microprocessor.

Zoot

Mike et al -- one clarification -- only the SX48/52 has that much RAM (16 banks of 16 registers). The SX20 and SX28 have 8 banks of 16 registers. And when using SX/B nearly two half-banks are "spoken for" for shadow registers, param variables, etc.

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Mr.Green

Why is it not possible to add RAM Mem. to the BS2 ?
Is it the physical size of the Address# ?

This is a very interesting POST

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The Truth is out there

Mike Green

The Stamps (all of them) have a Basic interpreter in them. The compiler for this Basic (the Stamp Editor), the interpreter (in the PIC or SX on-chip flash memory), and the interpretive code itself have no provisions for more than 26 bytes of variables. More space than that simply doesn't exist as far as Parallax Basic is concerned. There is the scratchpad RAM, but that's treated completely separately from the variables (with the GET / PUT statements). The chips themselves (the PICs and the SXs) also have no provisions for adding RAM. You can attach RAM as an I/O device (as you can with the Stamps), but it's not equivalent to the on-chip memory and can't be used the same way.

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Mr.Green

I Thank You for the clarity . I now have a new understanding of how things work.
This answers A lot of questions I've had


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The Truth is out there

John Mac

Thanks Mike for the good info....appreciate it