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DPRG: 80C51FA for the New Micro's NMIY-0031 SBC (!!! or ???)

Subject: DPRG: 80C51FA for the New Micro's NMIY-0031 SBC (!!! or ???)
From: Eric B. Olsen robojoc at worldnet.att.net
Date: Sun Jul 20 16:45:06 CDT 1997

Kipton Moravec wrote:
> (Oops wrong return address, sending from a friend's house.  This is the
> second try.)
> I have the New Micro's NMIY-0031 single board computer.  Has anyone
> tried to replace the 8031 with a 80C51FA?  It appears they have the
> identical pin out. (At least from looking at the Intel book, they have a
> Siemens chip installed). The 80C51FA has PWM for motor control (up to 4
> separate PWM types), a counter geared towards optical encoders, and a
> very accurate event timer (perhaps for acoustic distance detection). Oh
> by the way, the 80C51FA has 256 bytes of data RAM also, versus the 128
> bytes in the 8031. I think the 80C51FA costs less than $10 versus the
> 8031's $3.
> Has anyone tried to pull the processor out of the holder successfully
> (meaning without damaging anything). It appears to be a PLCC package and
> chip holder.  I am not familiar with the process.
> Regards,
> Kip


One of the main advantages with the 8031/8051 Intel architecture is the
existence of so many good derivatives offerd by third party
manufacturers.  Even Intel has it's share of decent derivatives like the

The main hardware difference that could stop one from using an 80C51FA
instead of an 8031 is IF an external clock source is used to drive the
CPU instead of using a crystal.  If a crystal is used on the New Micro's
board (and I'm betting it is), there shouldn't be any problem at all.  

Some 8031 designs use the lower cost NMOS chip as opposed to the modern
CMOS version chip (80C31).  If an external clock is used to drive an
NMOS 8031 CPU, the clock source is input to the XTAL2 input.  It appears
that all subsequent 80C51 and later designs use the XTAL1 input for
external clock drive.  

Again, if a crystal oscillator is used (instead of an external clock),
then your substitution should work just fine.  

There are versions of the 80C51FA that run faster (up to 16 Mhz), and it
you have one of these, you may consider changing the crystal frequency
to get the extra horsepower!  I find that 14.7456 Mhz crystals are a
good choice for 16Mhz type 80C51 parts as they are capable of producing
standard baud rates, and are about 50 % faster than the 11.0592 Mhz
crystals.  However, if you change the board frequency, factory ROMed
software will not communicate at the correct speed!

Pulling out PLCC chips from their carriers can be tricky.  If you
attempt to pry out the part using a screw driver at the corner of the
socket, you will almost certainly damage the socket and possibly bend
pins on the chip.  Use a PLCC extractor tool!  Digi-key offers a
universal extractor tool for $19.95 (K293-ND), and a low cost universal
extractor for $7.95 (although I haven't tried this one).  Even with the
tool, a bit of tugging and a little expereince is beneficial!

Good Luck,

Eric Olsen
Las Vegas, NV


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