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aka211
Joined: 24 May 2010
Posts: 15
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| Software SPI help !!! |
 Posted: Thu Jun 10, 2010 8:06 pm |
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I want to use software SPI, but I still have something not clear.
In the syntax #use spi(),
I've read that DI=pin " Optional pin for incoming data" so it's the data input pin but that's master data input or slave data input?
I wonder if DI pin have the same function as SDI in hardware SPI module ? or DI ~SDO ?
Anyone help me, plz ! |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Fri Jun 11, 2010 12:46 pm |
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| Quote: |
I've read that DI=pin " Optional pin for incoming data" so it's the data
input pin but that's master data input or slave data input?
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"DI" would be the input pin, for either Master or Slave. If it's configured
as a Master, DI is input. If it's configured as a Slave, DI is also the input.
But, software SPI should only be used for the Master. If you want to do
an SPI slave, then use the hardware module (SSP or MSSP). There are
dedicated pins on the PIC for the hardware SPI module.
| Quote: | | I wonder if DI pin have the same function as SDI in hardware SPI module ? |
Yes, that's right. "DI" is the same as "SDI". |
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aka211
Joined: 24 May 2010
Posts: 15
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| Posted: Sun Jun 13, 2010 9:18 pm |
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Thanks alot PCM !
So, if I config the pic16f946 as master use software SPI and a slave eeprom.
The DI pin of the PIC should be connected to SDO pin of the eeprom, right?
Like the picture above, RG1 will be DI pin?
Last edited by aka211 on Mon Jun 14, 2010 3:01 am; edited 4 times in total |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sun Jun 13, 2010 10:24 pm |
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I can't view your image, but yes, the DI pin on the PIC goes to the SDO
pin on the eeprom. |
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nahumof
Joined: 09 Apr 2011
Posts: 15
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| spi slave |
| Posted: Sat Apr 09, 2011 10:09 am |
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hi all
I'm intending to do some communication between 2 pics by software spi
so | Quote: | | software SPI should only be used for the Master |
then what is the use of #use spi(slave.......)? doesn't work as slave?
Does anybody have some code for an slave spi using software spi?
I was trying to do this
| Code: |
#int_ssp
void ssp_isr(void)
{
buffer[next_in] = spi_xfer();
next_in++;
if(next_in >= BUFFER_SIZE)
next_in = 0;
}
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At the slave with no results and I found this post:cry:
I guess it only work with spi_read();
regards
nahum  |
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temtronic
Joined: 01 Jul 2010
Posts: 9226
Location: Greensville,Ontario
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| Posted: Sat Apr 09, 2011 1:19 pm |
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if you don't get anywhere using SPI....
...you might consider just using the serial interface(aka RS232) for inter PIC communications.Fewer 'startup' headaches, easy to code,just as fast,examples in the examples folder..... |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sat Apr 09, 2011 2:22 pm |
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| Quote: | | I'm intending to do some communication between 2 pics by software spi |
Why ? Does your slave PIC not have an SSP module ?
Post the part numbers of your master and slave PICs. |
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dyeatman
Joined: 06 Sep 2003
Posts: 1934
Location: Norman, OK
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| Posted: Sat Apr 09, 2011 2:26 pm |
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One of them he is using has hardware (16F946 stated earlier).
_________________
Google and Forum Search are some of your best tools!!!! |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sat Apr 09, 2011 2:34 pm |
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Right, but there are two people on this thread. The first one is aka211
and the 2nd one is nahumof. aka211 is the one with the 16F946.
We don't know what nahumof is using. |
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dyeatman
Joined: 06 Sep 2003
Posts: 1934
Location: Norman, OK
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| Posted: Sat Apr 09, 2011 2:40 pm |
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Good point, I missed that... Switching posters in mid thread has caught me a few times.
_________________
Google and Forum Search are some of your best tools!!!! |
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nahumof
Joined: 09 Apr 2011
Posts: 15
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| Posted: Sat Apr 09, 2011 3:34 pm |
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ok tks for the reply
I'm using 18f4550 as master using software SPI works fine, and 16f876 as slave spi also sw fail.
I can't use hardware spi because its being used by another purpose in a already build pcb.
And I found this code for software spi but I want to use #use_spi or interrupt by ssp.
Code from Ttelmah
| Code: |
void send_spi_byte(int8 ClockPin, int8 DataOutPin,int8 val_to_send) {
int8 count;
for (count=0;count<8;count++) {
output_bit(DataOutPin, shift_left(&val_to_send,1,0));
output_high(ClockPin);
output_low(ClockPin);
}
}
int8 get_spi_byte(int8 ClockPin, int8 DataInPin) {
int8 count;
int8 val;
for (count=0;count<8;count++) {
output_high(ClockPin);
shift_left(&val,1,input(DataInPin));
output_low(ClockPin);
}
return(val);
} |
I could use #use_spi as pic slave?
tks  |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sat Apr 09, 2011 4:10 pm |
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The code you posted is for a software SPI master, not a slave. That code
generates the clock, and slaves don't make a clock. Only the master does
it. And, the code doesn't try to find the clock edge. A software slave must
do that, either by polling, or by triggering an interrupt on the clock edge.
And, #int_ssp is used only by a hardware SPI slave. But you said
you don't have the SPI hardware available.
With regard to #use spi() for a slave, here is a thread where I go through
it in detail. I noted that some bugs existed in the compiler version
available at that time. I haven't looked at it lately. It's possible that CCS
may have fixed it by now. What's your version ? My guess is, probably
4.093, etc. So it probably has bugs.
https://www.ccsinfo.com/forum/viewtopic.php?t=40421
------------------
Edit: Fixed link to point to correct thread.
Last edited by PCM programmer on Sat Apr 09, 2011 5:17 pm; edited 1 time in total |
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nahumof
Joined: 09 Apr 2011
Posts: 15
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| Posted: Sat Apr 09, 2011 4:46 pm |
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Yes of course I see that is master spi code | Quote: | | slaves don't make a clock |
I was meaning apply something like that for polling using ssp interrupt but now I'm aware | Quote: | | only by a hardware SPI slave |
so maybe the options is try polling with if cycles!!! 
yes my ccs version is 4.093
It seems I'm stuck  its also strange that anyone out there haven't try to make slave spi using software (different pin assignment).
Apologies for my bad english.
tks for all PCM I will try to make it work |
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nahumof
Joined: 09 Apr 2011
Posts: 15
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| Posted: Sat Apr 09, 2011 5:27 pm |
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tx for fix the link  |
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ckielstra
Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands
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| Posted: Sat Apr 09, 2011 8:26 pm |
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| nahumof wrote: | | It seems I'm stuck its also strange that anyone out there haven't try to make slave spi using software (different pin assignment). |
A SPI master in software is easy, but a SPI slave in software is a lot more work. That's why you find few examples.
Going back to the basics. Why do you want to use SPI and not use the UART as suggested earlier in this thread?
Do you have any pin available that can trigger an hardware interrupt in the slave? |
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