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DSP processor

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beenuseren

New Member
hi,

What is the difference among a Flash based, ROM based, RAM based microcontrollers? What does it mean if we say its a Flsh based controller?

Thanks
 

Sceadwian

Banned
Flash = memory stick style flash memory used to retrieve and store program code and data, ususally with supplementary ram for processing on the chip.

ROM = It's a masking process done during fabrication to program one program into the main chip, again likley with supplementary ram for processing on chip.

Not sure about RAM based chip, but it might refer to something like an FPGA where the entire device is based on RAM or ram like processing cells which need to be loaded from external ROM or FLASH. How exactly does this relate to DSPs? Because micro controllers are not DSPs. DSPs are usually 32bits with plenty of hardware accumulator and multipliers
 
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dknguyen

Well-Known Member
Most Helpful Member
It's just the difference between the memory type used in the microcontroller to store the program- so in that sense a RAM based microcontroller doesn't make too much sense. All microcontrollers have RAM in them to store run-time data.

Flash is cheaper, but can only be erased in blocks (of bytes) at a time. EEPROM is more expensive (and older) and any byte can be erased at any time. ROM means you can only program it once and afterwards it is permanent and you cannot erase (good for mass produced consumer goods). Since flash is cheaper you see more flash than ROM now, especially for microcontroller memory where you usually write over the entire thing and have no need to change "just one little bit of the program" already stored in memory.
 

Mikebits

Well-Known Member
RAM based devices are typically faster than Flash based. pitfall of RAM base is external memory is needed to load the uP, but once loaded the CPU can access memory faster.
 

Oznog

Active Member
Well, the reprogrammable ROM space may be called "ROM", "PROM", "EEPROM", "EPROM", or "flash" depending on who you ask.
In PICs, it must be block-erased, block size varies. Which doesn't matter really, no programmer that I know of even tries to program only the blocks that have changed when you recompile with a minor change.

There were UV-erasable programmable ROMs, but they've been mostly obsoleted for a long time. There were also ones which could only be programmed once and can't be erased, Microchip terms them "OTP" (One Time Programming). These are now obsolete.
 

Mikebits

Well-Known Member
The OP was not asking about PIC's.

Well, the reprogrammable ROM space may be called "ROM", "PROM", "EEPROM", "EPROM", or "flash" depending on who you ask.
What the heck does that mean? Type of memory is not just called whatever. Flash and EEPROM are very different. If you ask someone who knows what they are talking about, they would tell you explicitly what type of memory the device has.

If you have to read from FLASH, your system will be slower than reading from RAM. EEPROM's even slower, bottom line. Although I hear new FLASH devices are soon to come which boast high speeds.
 
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