copyright, Peter H. Anderson, Baltimore, MD, July, '98
Introduction.
The following discussion focuses on the SIMICE, a non real time
emulator which was developed
by RF Solutions and is a standard Microchip product.
In the discussion, I try to point out some of the limitations, but
offer that this package may be well
used to advantage by hobbyists as a "poor man's emulator" in developing
code for such
processors as the PIC16F84, 16C6 and C7 and if we ever see one, the 12C67
series.
This discussion was prompted by noting that Microchip was offering a
Web Promotion of $98.88
(regularly $129.00) "through your Microchip distributor". For most PIC
hobbyists, our distributor
is Digikey and to my knowledge, Digikey is not carrying this product.
This caused me to do a bit
of a search and I offer a discussion on how you might obtain one of these
packages.
I ordered one. But, to be quite honest, using the SIMICE isn't high on
my list of priorities. I am
now fortunate in that I have access to ICEPIC emulators and thus there is
no great incentive for
me to live with the shortcomings of the SIMICE. However, the price of an
ICEPIC is about $800
and not everyone has this kind of discretionary money.
However, I have been on the other side without an emulator. In the
Spring, '98 semester I had
some 35 eager undergraduates in a course on the PIC and they did quite
well with nothing more
than using their heads, using the simulator associated with the Microchip
MPLAB package, our
serial LCD (PIC-an-LCD) and lots and lots of programming and reprogramming
their PIC16F84s.
In particularly stubborn problems, I pulled out the one emulator we had
and usually found the
problem within a few minutes.
Thus, I know what it is like to work pretty much in the blind. My
concern, particularly for
newcomers is that working in the blind may lead to so much frustration
that they give up. This
SIMICE may be an answer for some people.
MPLAB Simulator.
The MPLAB Simulator is a marvelous tool and the price is certainly
right. It is free. It permits
you to set break points, single step, trace into, watch variables and the
like.
It suffers in that it is not real time and even a 10 msec delay may
take several seconds to execute.
This is easily corrected by using short delays and modifying them for the
real thing.
Handling inputs is about as painless as anyone could make it, but that
is still very painful. One
prepares a stimulation file. Myke Predko does a good job in treating this
in his book and I vividly
recall the words "makes your eyes bug out" in referring to the preparation
of these files.
Aside from your eyes bugging out, there is a problem in writing a
stimulation file to interface with
such devices as a DS1620 thermometer, 24LC65 EEPROM or LTC1298 A/D.
Chances are good
that you are not going to completely understand the data sheet and you are
going to spend a lot of
time writing an erroneous stimulation file. This is where we have found
the BASIC Stamp 2 very
helpful. We get a good understanding of the interfacing device using the
Stamp where changes
may be made in a few seconds and then we map the code over to a PIC.
SIMICE.
The SIMICE eliminates the need for the eye bugging preparation of
simulation files and permits
you to actually interface with the device you are using and thus solves
the two major problems
associated with the Simulator. You are actually interfacing with the real
thing.
It consists of a unit that hangs off a PC Serial Port and communicates
with the MPLAB
Simulator. Thus, I assume you use it quite like you may now use the
Simulator.
Frankly, I have been extremely impressed with Microchip in that they
seem to really want to sell
PICs and have done an outstanding job in developing and adopting quality
development tools that
are attractively priced and work. I was skeptical of the ICEPIC being
developed by RF Solutions
and MPLAB by Microchip, but the bottom line is there is a seamless
integration that makes the
whole thing pretty intuitive. The two companies seem to have a rather
unique close interface and
all the more unique in that there is a lot of land and water between the
two. I assume RF
Solutions and Microchip have done as good a job with the SIMICE.
The non-real-time aspect of the SIMICE of course may limit its use in
some applications; serial
routines and interfaces with the Dallas 1-wire devices come to mind. Just
how big a penalty this
is depends on your specific application. After all, many tasks are not
time critical. For example,
one might interface with a Dallas DS1602 elapsed time counter, Dallas
DS1624 temperature
sensor, Microchip 24LC65 EEPROM or Linear Technologies LTC1298 12-bit A/D.
Time is not
critical in any of these applications and this certainly is a lot of power
for less than $100.00 and
clearly, I have only scratched the surface in suggesting applications.
The Bad and Good News.
The SIMICE's capabilities are limited to the 12-bit core PICs (12C508,
509 and 16C5X series).
Of course, this is not bad news if your design target is a 12-bit core
PIC. I enjoy working with
students on PIC12C508 based designs, in part because they are a bit more
challenging than the
classic 16F84. And, the SIMICE really makes the PIC12C508/9 a bit more
practical for the
hobbyist. I think one could do quite well with the SIMICE, a few of the
windowed EPROM
devices and of course, a PIC-Start Plus programmer.
However, this 12-bit core limitation might appear a serious limitation
if your final target is a
PIC16F84. My point is that that the SIMICE may still prove a valuable
tool in testing and
debugging routines and then moving them from the 12-bit core to the
PIC16F84.
One might use the SIMICE with the target being the 12-bit core PIC16C56
which appears close
to the 16F84 which might be your final design target. Use the SIMICE to
develop various
routines to say interface with an ADC0831, LTC1298 or 24LC65 and similar,
test and debug
them and then move them to the PIC16F84.
The instruction set associated with the 12-bit and 14-bit core are very
close. As I recall, the
12-bit core lacks a few of the immediate instructions; e.g., ADDLW .1. I
encountered an
interesting problem in passing values back to a calling function in the W
register. For example;
MOVF VAL, W RETURN
Don't expect to find the value of VAL in W on returning to the calling
function. I have been told
that the RETURN with the 12-bit core is in fact a RETLW 0.
The 12-bit core uses the TRIS instruction to define the data direction
of I/O while the 14-bit core
requires using the RP0 and RP1 bits of the STATUS register to switch banks
and fiddle with the
appropriate TRIS register.
None of this is any too earth shattering. Admittedly, changes will be
required when moving
debugged code from a 12-bit core device to a 14-bit core PIC. However, it
is always the hardest
the first time. Over time, I am pretty sure it becomes second nature.
One irritation with the 12-bit core is a two level stack limitation and
I will confess I am inclined to
resort to rather poor programming practices in avoiding subroutine calls.
This can waste program
space. However, if you have the space, who cares. Another approach is to
use a user stack and
this is discussed in a Microchip application note and there is some
material on my PIC page. The
user stack will port from a 12-bit to a 14-bit core device.
The most confusing aspect of the 12-bit core is switching from one page
to another. However, if
you use the SIMICE with the idea of developing and debugging small chunks
of code, you can
avoid this by confining your code to page zero.
Finally, the 12-bit core devices have no interrupt capability.
And, there may be a few more subtle differences as well.
Note that the MicroEngineering Labs PICBASIC Pro does not support the
12-bit core devices
and thus cannot be used with the SIMICE.
By now, you are undoubtedly saying, "no way". But, there is nothing
more frustrating then
having say a PCF8574 8-bit I/O IC sitting there, not working and being
able to do no more than
stare at it and check and recheck your wiring. The SIMICE can open a lot
of options and save a
lot of frustration.
Of course, there is a penalty. There are small differences. If the
user stack bothers you, resolve
to limit your nesting to two and perhaps improve the quality of your code
when you move it to
the 14-bit core PIC.
If you find the page switching threatening, and I do, resolve to keep
your code on the SIMICE on
page zero.
Summary.
Certainly if your target processor is a 12-bit core device, the SIMICE
is a natural for anyone who
can't afford an ICEPIC emulator.
I will admit that when I first saw the SIMICE and discovered it was
limited to 12-bit core PICs, I
dismissed it. But, I have had some six months to think about it and over
four of those months I
was teaching some 35 undergraduates with no ICEPIC emulators. Looking
back, I did have
enough money to buy eight SIMICE systems. Had I been smarter and done so,
I could have
taught the 12-bit core, the use of something close to an emulator and how
to move a design from
one PIC to another and also avoided a lot of student and personal
frustration. But, we can never
go back. Rather we learn and go forward.
Indeed there is a bit of a learning curve in moving code from the
SIMICE to a 14-bit core PIC.
But, it sure beats staring at a non working circuit hour after hour and
giving up after a day or two.
I also have come to believe we learn best when we need knowledge. With
the SIMICE, there is a
powerful incentive to quickly learn the 12-bit core PICs and this adds to
your value. This value
may be a tangible benefit with your current or a future employer. But,
perhaps, it is simply the
personal satisfaction of knowing you accomplished something.
Availability.
When I first noted the promotion on Microchip's Web page, I was
excited, but I then realized my
"Microchip Distributor" and most hobbyist's distributor is Digikey and a
search on their web page
did not reveal that they have the SIMICE.
I did find it at Pioneer Electronics (http://www.pios.com). Look under
their Industrial Electronics
Div and do a search on the Microchip Part number DV162010. I assume Arrow
Semiconductor
(http://www.arrowsemi.com) also have it.
Unfortunately, many of these nationwide industrial suppliers (Arrow,
Pioneer, Bell Milgray, etc)
may not be too eager to do business with hobbyists. But, it doesn't hurt
to try. Find a local
Arrow and Pioneer office and give them a call.
If you are unsuccessful and really want one, send me e-mail and I will try to buy one for you. It will be $5.00 over the $98.88 web special (or $129.95 regular price) plus $4.00 shipping to you. The $5.00 covers the cost of me processing your credit card and the shipping to me. But, first try to buy it yourself as I have a monthly limit as to how much I can process on my merchant credit card account and I just about hit it each month in normal sales.