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rob norris
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| adjusting SPI speeds |
 Posted: Fri Oct 01, 2004 5:44 am |
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Hi, I believe I know why im having a problem interfacing a chip to my PIC. Alas, I do not know how to solve it.. The chip is supposed to signal a busy pulse after It successfully reads a byte send from the PIC (the byte is sent the same time a clock is generated).. However, the busy pulse is not being generated until the first bit of the next sent byte.. This picture will hopefully demonstrate:
[img]www.engr.mun.ca/~rob/stuff/help.GIF[/img]
I think the problem is im using the wrong clock edge (even though the manual for the chip im interfacing with says use the falling edge, which is what I am using).. But I guess i'll try the rising edge and see what I get.
The problem is, which I switch from:
setup_spi(SPI_MASTER | SPI_H_TO_L | SPI_CLK_DIV_16);
to
setup_spi(SPI_MASTER | SPI_L_TO_H | SPI_CLK_DIV_16);
I loose control of the clock speed, and differing the CLK_DIV_# has no bearing when I put it on the second mode... Does anyone know why this could be happening?
I need to set the clock to somewhere between 500kHz and 2Mhz, (I'm using a 20Mhz crystal on a PIC18F452)..
Does anyone know how to fix my problem?? Thanks! |
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Neutone
Joined: 08 Sep 2003
Posts: 839
Location: Houston
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| Posted: Fri Oct 01, 2004 7:04 am |
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| Do a search for SPI_CLK_DIV_16 in your headder file. You will find the slower settings there. |
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rob norris
Guest
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| Posted: Fri Oct 01, 2004 7:08 am |
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| I have tried the other speed selections, however they do not change the frequency when I am using SPI_L_TO_H mode. The frequency stays locked at 1.25Mhz no matter what DIV I use. |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sun Oct 03, 2004 11:08 am |
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| Quote: | The problem is, which I switch from:
setup_spi(SPI_MASTER | SPI_H_TO_L | SPI_CLK_DIV_16);
to
setup_spi(SPI_MASTER | SPI_L_TO_H | SPI_CLK_DIV_16);
I loose control of the clock speed, and differing the CLK_DIV_# has no
bearing when I put it on the second mode...
Does anyone know why this could be happening? |
Compile the test program below, and then post the portion of the .LST
file which begins at main().
More questions:
1. What version of the PCH compiler are you using ?
2. How are you measuring the frequency of the SCLK signal ?
Are you using an oscilloscope ?
3. Also, just to be sure, what pin on the PIC are you probing
when you do this ?
4. What test program are you using to generate an SCLK signal
when you measure it ? You should be using a program similar
to the one that I posted in this thread. It's very simple and all
it does is put out a data stream and clock. That's the kind of
program you need to be using when you test the clock speed.
http://www.ccsinfo.com/forum/viewtopic.php?t=20520
#include <18F452.h>
#fuses HS, NOWDT, NOPROTECT, BROWNOUT, PUT, NOLVP
#use delay(clock = 20000000)
//====================================
void main()
{
setup_spi(SPI_MASTER | SPI_H_TO_L | SPI_CLK_DIV_16);
setup_spi(SPI_MASTER | SPI_L_TO_H | SPI_CLK_DIV_16);
while(1);
}
This is the code produced by the above program for PCH 3.188.
Please post the same block of code from your .LST file, after
you compile it.
| Code: | 0000 00294 .................... void main()
0000 00295 .................... {
0004 FFFF 00296 NOP(FFFF)
0006 6AF8 00297 CLRF FF8
0008 9ED0 00298 BCF FD0.7
000A 6AEA 00299 CLRF FEA
000C 6AE9 00300 CLRF FE9
000E 0E06 00301 MOVLW 06
0010 6EC1 00302 MOVWF FC1
0000 00303 ....................
0000 00304 ....................
0000 00305 .................... setup_spi(SPI_MASTER | SPI_L_TO_H | SPI_CLK_DIV_16);
0012 9AC6 00306 BCF FC6.5
0014 9A94 00307 BCF F94.5
0016 9694 00308 BCF F94.3
0018 0E21 00309 MOVLW 21
001A 6EC6 00310 MOVWF FC6
001C 0E00 00311 MOVLW 00
001E 6EC7 00312 MOVWF FC7
0000 00313 ....................
0000 00314 ....................
0000 00315 .................... while(1);
0020 EF10 F000 00316 GOTO 0020
0000 00317 .................... } |
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