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Backfire
Joined: 12 Oct 2020
Posts: 46
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| I2C Poll Function |
 Posted: Wed Sep 15, 2021 2:37 am |
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Morning (from where I sit) everyone,
I've a quick question I was looking for some background information on.
I'm running a PIC18F25K20 which is attempting to talk to a PIC16F1512 over I2C. I *have* got them passing some bytes, but I'm hoping someone can review my logic, in order to improve the reliability of the comms, which are a little sporadic in their current operation.
My sending code is;
| Code: |
Buffer[0] = 0b10000000 + ID;
//fprintf(SERIAL, "Buffer: %X\r", Buffer[0]);
while(!I2CDeviceReady(0x20));
I2CACK = i2c_transfer_out(0x20, Buffer, 1);
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And my receiving code is;
| Code: |
if(i2c_poll())
{
output_high(LED);
index = 0;
{
buffer[index] = i2c_read();
index++;
}while(i2c_poll());
fprintf(CONFIG, "Buffer:%s\r", buffer);
}
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This triggers the printf statement in the reception code twice, while I would've only expected it to trigger once, with all the bytes collected from the iterative i2c_read() calls?
My implementation is at the limit of device memory, so I'd prefer to avoid the ISR route, as this code only needs to collect a maximum of two bytes over I2C, (after receiving the address, that is).
Hoping someone can see the flaw in my logic! Many thanks in advance. |
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Backfire
Joined: 12 Oct 2020
Posts: 46
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| Posted: Wed Sep 15, 2021 3:29 am |
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I also see in a 'Newsdesk' article on CCS's news page that they post an example usage of an i2c function as:
| Code: | | i2c_transfer_out(EEPROM_STREAM, 0xA0, &rAddress, 1); |
Whereas in the example files there is also an implementation as such:
| Code: | | i2c_transfer_out(I2C_SLAVE_ADDRESS, buffer, 1); |
I'm curious as to what the difference is here, as I suspect it's where my lack of understanding is causing my issues. |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19509
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| Posted: Wed Sep 15, 2021 3:49 am |
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Remember a transfer sends the target address, then the data.
So poll will go true, when the address byte is received, and then again for
the data byte. |
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Backfire
Joined: 12 Oct 2020
Posts: 46
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| Posted: Wed Sep 15, 2021 3:54 am |
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Hi Ttelmah,
thanks for your reply. I seem to be getting 3 triggers of my printf(...) statement though, when my sending code is as described:
| Code: | | I2CACK = i2c_transfer_out(0x20, Buffer, 1); |
Whereas I'd expect two executions, based on the address reception, and then the data byte? |
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Backfire
Joined: 12 Oct 2020
Posts: 46
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| Posted: Wed Sep 15, 2021 4:00 am |
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After altering my code to dump my intended reception buffer, this is the output upon the I2C being sent the data byte. So the i2c_poll() triggers three times seemingly.
| Code: |
Buffer[0]:
Buffer[1]:<NUL>
Buffer[2]:<NUL>
Buffer[3]:<NUL>
Buffer[4]:<NUL>
ID:0
Buffer[0]:
Buffer[1]:<NUL>
Buffer[2]:<NUL>
Buffer[3]:<NUL>
Buffer[4]:<NUL>
ID:0
Buffer[0]:[Warning: "81h 0Dh" is a byte sequence outside the Unicode basic multilingual plane (plane 0)! Only Unicode plane 0 is supported by .NET Framework and thus YAT (yet).]
Buffer[1]:<NUL>
Buffer[2]:<NUL>
Buffer[3]:<NUL>
Buffer[4]:<NUL>
ID:0
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Backfire
Joined: 12 Oct 2020
Posts: 46
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| Posted: Wed Sep 15, 2021 4:38 am |
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Even separating the i2c_read()'s accross multiple functions, I still seem to be 'collecting' the address byte twice. I've now divided my code thusly:
In main() loop:
| Code: |
if(i2c_poll())
{
if(i2c_read() == 0x20)
{
output_high(LINK_LED);
BoardCmd = GetI2CCommand();
}
fprintf(CONFIG, "Board:%x\r", BoardCmd);
}
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Where:
| Code: |
int8 GetI2CCommand(void)
{
int8 index = 0;
char buffer[5] = {0};
while(i2c_poll())
{
buffer[index] = i2c_read();
fprintf(CONFIG, "Buffer[%u]:%x\r", index, buffer[index]);
index++;
}
return 0xA1;
}
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But, my debug dumps are showing the I2C address seemingly being collected again:
| Code: |
Buffer[0]:20
Buffer[1]:81
Board:a1
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Shouldn't the read() in the address-checking function call clear the register for Buffer[0] == 81?
Apologies if I'm missing something simple! |
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