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Replaceing PIC processors with SX's


SX processors have been used to replace PIC 16C57's and 54's useing the .hex file from MPLab (renamed to .shx and programmed with the SX-Key or SXDev). You will need to play with the oscillator settings and you should change the capacitor values and add a carbon compisition resistor as per the clock requirements listed in the SX datasheets.

In the full PIC compatibility mode, expect power consumption at 5 volts to be 40 mA or so at 20Mhz compaired to 9.5 mA for the 57's. BUT... If you switch the SX chips to turbo mode (4x pipeline) and change the clock to 5Mhz, the power will drop to about 9 or 10 mA and the code MAY continue to run correctly. I've seen some code stop working but most work just fine. Its the pipelining that can cause small timing variations which sometimes affect very sensitive code. If you need to adjust a timing issue, it isn't that hard to migrate the code... see below.

Why replace a PIC with an SX if the power usage is the same at best? The SX chips will run at 3.3 volts (about 4 to 5mA at 5Mhz) and the PICs currently do not...
... at least not at anything like a reasonable clock rate. Now, Some PIC's do a version of low voltage and some do not. All the SX's do. Since I looked at them, Microchip has come out with a new version of the 16C57 that DOES support down to 2.5 volts.... Look at the datasheet for the maximum clock speed for different values of Vdd.

Vdd  Max Clock
4.5v 20 MHz
3.0v  4 MHz
2.5v 40 kHz

That is 40 KILO Hertz at 2.5 volts.

I think you will find that most PICs are in the same boat.

Now, the Ubicom SX28AC50 will do 32Mhz at 2.7v and 50Mhz at 3.0v AND because of the 4:1 pipeline that is the approximate equivalent of the PIC doing 128Mhz or 200Mhz.

But a more likely reason to switch to SXing is that; damn the power, you need more speed than the PIC can supply! If your PIC is bit banging 9600 baud and you need 19200, just drop in an SX in non-turbo (compatibility) mode and double the clock. No code re-write, no upgrade to a PIC with hardware UART, just make sure the power supply can take it.

If you really want to move to SXing...

* Yes you can use MPLAB (just tell it you are programming a 16c54) with macros for the extra instructions but you won't be able to make use of the in circuit debugging from MPLAB.  You can use the SXKey for the ICD and use macros to make it understand MPLAB style instructions. See:
http://www.sxlist.com/ubicom/inst.htm for details

Also:

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file: /Techref/scenix/picreplace.htm, 4KB, , updated: 2013/7/23 11:31, local time: 2014/10/31 04:11,
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