Many people would like to use PAKs that use SHIFTIN/SHIFTOUT with Pic Basic from MELabs. You can do this, but there are a few things you need to know.
The problem is that the ShiftIn/ShiftOut command is too fast on some versions of PIC Basic. This will depend, too, on the speed of the PIC you are using.
One answer is to use the "roll your own" approach, and write your own substitutes for ShiftIn/ShiftOut as shown in the PAK manuals (for the Stamp I). Make sure you have enough time between pulses (the value depends on the type of PAK -- read PAK Interfacing for more details.
You might think that you could use DEFINE SHIFT_PAUSEUS, however that is broken in some versions of PIC Basic. If it is ever fixed, this should work fine. However, the current workaround suggested by MELabs is to open up PBPPIC14.LIB and find the line that reads:
goto $ + 1 ; Slow down transfer
Add some more lines of "goto $+1" just below that. Each line will add 2uS at 4MHz (scale for your clock rate). So:
goto $ + 1
goto $ + 1
goto $ + 1
goto $ + 1
Would add 8uS to the already 2uS that is there for a total of 10uS. However, recent versions (version 2.40, at least) account for your clock speed correctly, so there is no need to worry about it. Typically, you'll need to make the following changes to our Basic Stamp libraries:
|Change the I/O pin definitions to match what you are using|
|Change any nibble variables to bytes|
|Add any specific defines you need for PBP|
|If you are running a fast PIC you may need to add some delay into the FReset command, and perhaps other commands that might need a little time to execute. However, PAKs that have functions take a long time to execute usually handle that by indicating when they are done (for example, math functions on a PAK I, II, or IX).|
|Include modedefs.bas (part of PBP) to define things like MSBFIRST, etc.|
For the maximum control, you can "roll your own" SHIFTIN and SHIFTOUT commands. Here's an example:
pakclock con 3 ' 6us @ 20MHz (adjust for your clock) pakclocklow con 3 ' 3uS low 6uS + 3uS + 1uS hold = 10uS = 100kbps shiftoutput: ' sends iobyte output datapin for i=0 to 7 ' Set data pin to 0 or 1 low datapin if (iobyte & $80) <> $80 then goto so0 high datapin so0: iobyte=iobyte<<1 ' shift byte left pauseus pakclocklow pulsout clk,pakclock pauseus 1 next pauseus 50 ' give it some time to process return shiftinput: input datapin iobyte=0 for i=0 to 7 iobyte=iobyte<<1 ' shift left iobyte=iobyte | datap pauseus pakclocklow pulsout clk,pakclock pauseus 1 ' hold data a tick next return
You need to adjust the pakclock and pakclocklow constants to match your processor speed and the speed of the PAK. The code above works for a 50MHz PAK.
As an example, here is the PAK-VIII library converted to PIC Basic Pro (this library appears on the product disk since April 25, 2002). You can also find a PAK-VII library that uses "roll your own" SHIFTIN and SHIFTOUT commands on this page. There is also a PAK-I library that would be easy to adapt to the PAK-II or IX (since the PAK-II and IX are based on the PAK-I).
' These are some starter routines ' that will help you use the PAK-8 ' Coprocessor from AWC ' For PIC Basic Pro V2.40 Include "modedefs.bas" define LOADER_USED 1 ' comment this out if not using a boot loader Define OSC 20 ' change to suit your speed ' Change these to suit your setup datap var portc.2 ' Data pin (I/O) datapin var portc.2 clk var portc.3 ' Clk pin (output) ' Register names DURLOW con %000 DURHIGH con %001 HIGHDUR con %010 LOWDUR con %011 PSCALE con %100 PSBASE con %101 N con %110 CTRL con %111 output clk output datap fpx var word ' Integer used by some routines fpb var byte ' byte ' parameters for FCommand chan var byte register var byte gosub freset ' always reset! ' TEST CODE -- REPLACE WITH YOUR OWN ' This program blinks an LED on the PAK's port 0 at 1Hz t: gosub FTotalReset ' hard reset top: chan=0 register=1 fpx=50000 ' 500 ms on and off = 500ms period = 1Hz gosub FCommand register=2 ' no need to set register again gosub FCommand ' turn on pulse operation of channel 0 fpb=3 gosub FJam stopit: goto stopit ' End of your code -- everything from here down is library code ' Reset the Pak8 I/O FReset: LOW DATAP LOW CLK pauseus 50 ' might be able to reduce these pauses if necessary HIGH CLK pauseus 50 HIGH DATAP pauseus 50 LOW CLK pauseus 50 return ' 0 is 0, 1 is 1, 2 is hi-z, 3 is normal ' note: 3 enables channel to run! FJam: fpb=chan + (fpb<<3)+%01000000 goto FSendByte FCommand: ' inputs chan = channel, register = register fpb=(register<<3) + chan gosub FSendByte fpb=fpx.lowbyte gosub FSendByte fpb=fpx.highbyte goto FSendByte FReadReg: fpb=(register<<3) + chan + %10000000 gosub FSendByte ' fall into FReadWord FReadWord: Shiftin datap,clk,MSBPRE,[fpx.lowbyte,fpx.highbyte] return FTotalReset: fpb=$FF FSendByte: Shiftout datap,clk,MSBFIRST,[fpb] return FReadByte: shiftin datap,clk,MSBPRE,[fpb] return FPrescale: ' set fpb to the prescale constant fpb = fpb + $C0 goto FSendByte
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