Microcontroller Selection 1

[mmilbury]

I've identified a few things that I need to know when selecting a microcontroller.

• Number of pins
• ADC converters
• DAC?
• Interrupts
• Internal/External Memory
• SCSI compatable
• Anticipated production dates (i.e. is chip expected to be discontinued?)
• Price
• Assembly Language/Ease of use
• Programmer available?

Have I left anything out? Would anyone know any online resources on chip selection that I might be able to use? ? ?

Thanks for reading what I've written. ----
An optimist sees the cup half full
A pessimist sees it half empty
An engineer sees it twice as large as it needs to be.

 

[Lewish]

Hello,
I do not know of any SCSI compatible microcontrollers. SCSI is a microcontroller all to itself.
When you say number of pins, I assume you mean number of I/O pins. Otherwise, do you really care how many pins the package has?
For my applications, I prefer a micro that is compatible with C programming, i.e., it has a built-in hardware stack.
I also like micros that have built-in flash memory that is JTAG programmable.
I also like to consider a micro family that has a masked-ROM option in case the product goes to high volume.

Anything else????

 

[mmilbury]

awesome post. . thanks. .

What I meant by SCSI compatable was being able to hook it to my computer. I'm not familiar with JTAG, though.

Finally my understanding of masked-ROM is it prevents reverse engineering so people won't be able to see my program after I've done it. Is this correct?

Thanks again ----
An optimist sees the cup half full
A pessimist sees it half empty
An engineer sees it twice as large as it needs to be.

 

[Lewish]

You are right, a masked-ROM can not be read by normal means. If you have a Class 2 clean room and a wafer probe, you could reverse engineer it, but is it worth the costs??
JTAG is much easier and a more universal connection between a computer and a microcontroller. It does require a JTAG module, which usually connects to the serial port, but some connect to the parallel port. If you have flash memory and a JTAG you can program you micro and read back its RAM and ROM while running in emulation mode. Very useful for program debug.
Another point about masked-ROM, it is cheaper in volume. For example, I am using a micro which costs $9.00 at 10,000 piece pricing and I have to spend another $1.00 to program it. When we convert to a masked-ROM, it will cost $2.98 at 10,000 pieces + a $5000 NRE charge. Quite a savings.

 

[Chancy99]

Actually, a masked ROM is easier to shave and read than a flash-based system. Manually reading flash is much more difficult, or so I've been led to believe ...

Hooking to your computer can be done via many means. Simplest (relatively) is probably just with a serial interface - many micros have a simple RxD/TxD serial interface. Hook that to a MAX3235 type interface chip, and you have normal serial.

Alternatively, you can hook the RxD/TxD pins to a FTDI 232 USB chip. The micro still talks normal serial, and the 232 translates to USB. You can use their 245 to use an 8-bit parallel interface instead if you have the IO pins to spare.

Go with JTAG if you can. Makes debugging much easier. Including either ISP (In System Programming) or some method of bootloader for later updates of firmware is a good idea as well.

Me personally, I like the AVR line from Atmel. Check out

http://www.atmel.com

or

http://www.avrfreaks.net

Dean.

 

[repoman]

Wait a sec!
You covered all your basis for microcontroller requirements, but why would you use an external scsi port when your computer has USB, parallel, and serial ports? These are much more documented and MUCH EASIER to work with than SCSI.