 |
 |
| View previous topic :: View next topic |
| Author |
Message |
vtrx
Joined: 11 Oct 2017
Posts: 144
|
| Setup Hardware SPI |
 Posted: Fri Jul 16, 2021 7:45 pm |
 |
|
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) |
|
|
 |
PCM programmer
Joined: 06 Sep 2003
Posts: 21708
|
|
| Posted: Sat Jul 17, 2021 10:52 am |
|
|
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)
|
The code above is using the hardware SPI registers. |
|
|
Ttelmah
Joined: 11 Mar 2010
Posts: 19966
|
|
| Posted: Sun Jul 18, 2021 12:29 am |
|
|
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. |
|
|
PCM programmer
Joined: 06 Sep 2003
Posts: 21708
|
|
| Posted: Sun Jul 18, 2021 3:38 am |
|
|
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);
}
|
It does two sequential 8-bit transfers to get 16 bits. |
|
|
Ttelmah
Joined: 11 Mar 2010
Posts: 19966
|
|
| Posted: Sun Jul 18, 2021 4:11 am |
|
|
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. |
|
|
vtrx
Joined: 11 Oct 2017
Posts: 144
|
|
| Posted: Wed Jul 21, 2021 9:21 am |
|
|
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);
} |
|
|
|
|
|
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
|
Powered by phpBB © 2001, 2005 phpBB Group
|
FAQ 
Search
Register
Profile 
Log in to check your private messages 
Log in
