Opinions ......... PIC microcontrollers verses the SX range

duffling

Im just curious ......

im currently using the Basic stamp controllers and love them .. thinking of moviing the SX programmer

but .. im still lured toward the PIC controllers ......

any opinions as to which is better .. im planning on fairly complicated programs for MIDI applications


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Paul Baker

Check out my reply in this thread http://forums.parallax.com/showthread.php?p=529575

There is no nudging here, it was in the Basic Stamp Forum in response to a question asked regarding quadrature encoders, so I wouldn't have expected you to have read this post to try and find an answer to your question.

my suggestion is to get the user manual for the SX, a few PICs and a few Atmel microcontrollers and do a side by side comparision of each of them. They all have thier strengths and weaknesses, It all depends on you application and a host of other factors. To my knowledge the SX is the only one that has a free and well supported BASIC compiler.

Post Edited (Paul Baker) : 3/21/2005 5:21:55 PM GMT

duffling

ok i read thru that thread ..

the only thing that worries·me about the sx28 is the limited program storage memory . 2k i belive and 4 k on the newer models

some of the PICs have 16k +

my programs will be getting quite advanced ...... and i imagine ill be needing some space to add the features i want

i understand external EEPROMS are only for data storage which i will need .. but im worried i wont fit my code in the 2k space of the sx28

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Forrest

Here's an SX based computer with 128K of SRAM www.xgamestation.com/view_product.php?id=12

Paul Baker

I honestly prefer the Atmel Mega series over the PIC series, this may just be a personal preference, but they seem to have better features over the PIC. Judge for yourself:

Atmel Parametric Table:
http://www.atmel.com/dyn/products/param_table.asp?family_id=607&OrderBy=part_no&Direction=ASC

PIC Parametric Table:
http://www.microchip.com/ParamChartSearch/chart.aspx?branchID=1005&mid=10&lang=en&pageId=74

though the PIC18F series is pretty attractive. The super sweet feature the megas have that gets me is the across the board incorperation of a hardware multiplier, this feature is ussually only availible in DSPs but a quick of the most expensive PIC shows it has one too, though I don't know at which point this feature becomes standard.

Post Edited (Paul Baker) : 3/21/2005 6:41:34 PM GMT

Guenther Daubach

duffling,

please have a look at www.parallax.com/sx/projects/projects_pwm.asp. There you find the description of one of my most complex SX28 applications I did so far, and there is still some free program memory, and a few free bytes in RAM memory. I doubt that I could have done the same project with just one PIC.

All these tasks are handled by one single SX28:

- Controlling the speed of three DC motors via PWM including a "soft start"
- Controlling the direction of the motors via three output lines
- Counting tacho pulses generated by the three motors
- Controlling the position of the motors by comparing the tacho counts and target values
- Checking for motor over-current situations
- Checking for stuck motors
- Checking two end-position sensors for one motor, and two reference sensors for the other motors
- Acting as an I²C slave to receive position data and commands, and to return the current status
- Controlling an on-board status LED
- Automatic "search for reference point" mode
- Checking for timeouts, i.e. when no more commands are received via I²C within a certain period of time, all motors are stopped

The available program memory would even allow to control one more motor but the SX 28 does not have enough I/O pins for that but an I/O expander could have done the trick. Fortunately, my customer later decided that thee motors were enough.

As you can see, a lot can be done with just 2 K words of program memory.

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Greetings from Germany,

Günther

Jon Williams

In the end, it's a personal preference thing. There are lots of interesting microcontrollers on the market. If you do choose the SX, you get the support of Parallax and cool dudes like Guenther -- you don't find that with all other vendors.

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Jon Williams
Applications Engineer, Parallax
Dallas, TX· USA

Paul Baker

Jon Williams said...
In the end, it's a personal preference thing. There are lots of interesting microcontrollers on the market. If you do choose the SX, you get the support of Parallax and cool dudes like Guenther -- you don't find that with all other vendors.

That is so true, it was wandering onto the forums and seeing such an active community and·good support by Parallax staff that "sealed the deal"·in deciding to adopt the SX as my preferred development platform. There is nothing more exasperating than being stuck and having nowhere to turn for help.

hmsmith

The SX family are unusally fast microcontrollers but are unusually stupid - particularly with I/O.

Most 8 bit micros run below 10 MIPs, the SX can run 50-75 MIPs.

Many 8 bit micros (but not all) have·larger internal memory RAM and·ROM/Flash than the SX.

In terms of internal memory and I/O pins, the SX·is fairly expensive (compare Microchip PIC).

Most 8 bit micros include peripherals such as UARTs, SPI or IIC interfaces, multifunction timers.

Some 8 bit micros have an external bus that can access additional RAM/ROM and other peripherals.

Because of its speed, the SX can easily perform UART, SPI/IIC, timer functions, access external devices,·and implement other standard and non standard interfaces in software rather than relying on built in hardware.

Writing software I/O devices (even with the SX virtual peripheral code available) will be a challenge for a beginner.

Once you know what hardware I/O·you need for your project, you should see·what devices have some or all of the peripheral you need and sufficient memory for your application, and compare that to and SX.

The first project I did with an SX part required interfacing to a SmartMedia memory card and I2S digital audio serial output at several megabits per second, and decompressing four audio channels.

I could not find a suitable micro·directly supported SmartMedia or I2S and the SX was the only micro fast enough to perform the decompression. It does a great job for me and was well worth the effort.

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duffling

Great .. thanks for the replys .. most helpful

I will probably purchase the SX very soon and attempt to learn assembly with this tool ....... i assume this knowledge can be applied to almost any microcontroller

and having this forum around will be a great help!

does anyone have any resources for suppliers of SRAM? just thinking well ahead .. i wish to read up about this
how its used with microcontroller etc..

thanks again..
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Paul Baker

duffling said...

I will probably purchase the SX very soon and attempt to learn assembly with this tool ....... i assume this knowledge can be applied to almost any microcontroller

yes though each architecture has its own set, once you learn one it is only an incremental step to learn another.

does anyone have any resources for suppliers of SRAM? just thinking well ahead .. i wish to read up about this
how its used with microcontroller etc..

my current fav is the CY7C1019B-15VC an 128Kx8 15ns for under $4 at digikey, though there are many other types availible that would work equally as well. An SX28 does not have enough IO pins to interface with it (28 required to address all locations) but using a couple latches it is possible to·interface with one. One of my first posts was describing how to do this. I'll send you the link to the post in an IM when I have some time to track it down.