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vtrx
Joined: 11 Oct 2017
Posts: 142
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| Setup Hardware SPI |
 Posted: Fri Jul 16, 2021 7:45 pm |
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To use SPI by hardware from 18f2550/4550, just declare it like this?
| Code: | void main(void
{
...
setup_spi(SPI_MASTER|SPI_L_TO_H |SPI_XMIT_L_TO_H|SPI_CLK_DIV_16);
... |
How do I change to 16bit to match this one?
| Code: | | #use SPI(DO=PIN_A0,DI=PIN_A3,CLK=PIN_A2,MODE=0,BAUD =270000,BITS=16,msb_first,SAMPLE_RISE,STREAM = max7912) |
Using the configuration below, will i be using the hardware?
| Code: | | #use SPI (MASTER,SPI1,baud=1000000,MODE=0,BITS=16,msb_first) |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sat Jul 17, 2021 10:52 am |
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It should. To confirm it, look at the .LST file in symbolic mode.
You should see something like this:
| Code: |
.................... #use SPI (MASTER,SPI1,baud=1000000,MODE=0,BITS=16,msb_first)
0004: MOVF SSPBUF,W
0006: MOVFF ??65535+1,SSPBUF
000A: RRCF SSPSTAT,W
000C: BTFSS STATUS.C
000E: GOTO 000A
0012: MOVF SSPBUF,W
0014: MOVWF @01
0016: MOVFF ??65535,SSPBUF
001A: RRCF SSPSTAT,W
001C: BTFSS STATUS.C
001E: GOTO 001A
0022: MOVFF SSPBUF,00
0026: GOTO 0054 (RETURN)
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The code above is using the hardware SPI registers. |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19515
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| Posted: Sun Jul 18, 2021 12:29 am |
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You'll be using the hardware, but not on the pins listed.
SPI1 on the 2550/4550, uses pin B0 for SDI, C7 for SDO and B1 for SCK.
setup_spi, cannot do 16bit transfers.
If you read the manual for #use SPI, you will find no reference to
setup_spi, spi_read or spi_write.
setup_spi, is designed to be used with spi_read and spi_write, and is the
'older' way of setting up the SPI. It only supports the hardware, and therefore
8bit transfers.
#use SPI, is the later setup for SPI. It is designed to be used with spi_xfer,
not spi_read/write. This command brings with it the capability for up to
32bit transfers, by automatically performing multiple transfers.
So your #use SPI, will be using the hardware, on pins B0, C7 and B1,
but to perform 16bit transfers the code will have to change and use
spi_xfer, rather than spi_read/spi_write. |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sun Jul 18, 2021 3:38 am |
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I didn't post my source code for that listing. Here it is:
| Code: |
#include <18F4550.h>
#fuses HS, NOWDT
#use delay(clock=20M)
#use SPI (MASTER,SPI1,baud=1000000,MODE=0,BITS=16,msb_first)
//=================================
void main()
{
spi_xfer(0x1234);
while(TRUE);
}
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It does two sequential 8-bit transfers to get 16 bits. |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19515
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| Posted: Sun Jul 18, 2021 4:11 am |
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Yes. The key is that PCM correctly used the SPI_xfer... 
I read it PCM, that he is changing something in some existing code
that used setup_spi. Hence it is vital to realise that he needs to change
both the #use, and the actual I/O function used. |
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vtrx
Joined: 11 Oct 2017
Posts: 142
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| Posted: Wed Jul 21, 2021 9:21 am |
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Thanks for the answers.
Both 'setup_spi' and "#use SPI (MASTER,SPI1..." use the hardware, but i'm using "setup_spi" because I can choose the speed following the datasheet(4,16 and 64), using "#use SPI (MASTER..." ,i don't know if the speed is that shown in BAUD.
Here are the changes that were needed:
| Code: | void main(void
{
...
setup_spi(SPI_MASTER|SPI_L_TO_H |SPI_XMIT_L_TO_H|SPI_CLK_DIV_16);
... |
| Code: | void sendData(unsigned int16 data)
{
output_low(CS);
spi_write(make8(data,1));
spi_write(make8(data,0));
output_high(CS);
}
.....
void skip_data()
{
spi_write(0x00);
spi_write(0x00);
} |
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