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Manu59114
Joined: 22 Jan 2018
Posts: 34
Location: North of France
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| 1 wire Dallas CRC for PCD |
 Posted: Wed Oct 03, 2018 11:55 am |
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Hello to all
I use with success the 1 wire CRC code for a serial communication between 2 PIC18. Very fast code to calculate the CRC !a
Now i would like to interface a board using a dsPIC33EP512MU810 (PCD)
and i was thinking that i used the code from ckielstra found on this topic:
https://www.ccsinfo.com/forum/viewtopic.php?p=60194
As we can see, the code was defined for PCM and PCH but not for PCD
| Code: |
#if defined(__PCM__) // For example (and tested on) PIC16F74, PIC16F887
#byte FSR = GETENV("SFR:FSR")
#byte INDF = GETENV("SFR:INDF")
#elif defined(__PCH__) // For example (and tested on) PIC18F4520
#byte POSTINC0 = GETENV("SFR:POSTINC0")
#else
#Error You need to setup the above for your PIC Chip
#endif
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Is there someone that used this code for PCD?
What would be the code for GETENV for PCD?
Many thanks for your reply!
Wish you all the best!
Manu
_________________
CCS + ICD3 + PIC18F46K80 |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19830
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| Posted: Wed Oct 03, 2018 12:18 pm |
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You would not use the same method.
On the DsPIC, the actual XOR instruction, can use any register as it's source address (or destination), and increment either. So unlike the lesser PIC's where you have to load with indirect addressing, then do the maths, on these the maths and the fetch can all be done in one instruction!.. So you just load a register with the address to use as the source, and the fetch and first XOR, become. So perhaps W2 as the working register, and W3 as the address, gives:
XOR.B W2, [W3++], W2
would replace all of:
| Quote: |
#if defined(__PCM__)
movf INDF, W // load W with next databyte
incf FSR // do a 8-bit increment - increment indirection register to point to next databyte - for the next time
#elif defined(__PCH__)
movf POSTINC0, W // load w with next databyte and increment indirection register to point to next databyte - for the next time
#else
#Error You need to setup the above for your PIC Chip
#endif
xorwf crc, F
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Manu59114
Joined: 22 Jan 2018
Posts: 34
Location: North of France
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| Posted: Wed Oct 03, 2018 1:47 pm |
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Thanks Ttelmah,
I will test tomorrow!
MAnu
_________________
CCS + ICD3 + PIC18F46K80 |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19830
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| Posted: Thu Oct 04, 2018 12:37 am |
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I've put together a basic PCD version of this:
| Code: |
#INCLUDE "33EP512MU810.H"
#device PASS_STRINGS=IN_RAM
#fuses NOWDT
#use delay(internal=64MHz)
#PIN_SELECT U1TX=PIN_D1
#PIN_SELECT U1RX=PIN_D0
#use RS232(UART1, baud=9600)
#include <string.h>
unsigned int8 crc;
//-----------------------------------------------------------------------------
// This is the crc8 function for use on the PIC16 and PIC18 etc. microprocessors
unsigned int8 Calc_Crc8(unsigned int8 *p_data, unsigned int8 datalength, unsigned int8 crc)
{
#asm
MOV p_data, W3
CLR WREG
MOV.B crc, WREG
MOV WREG,W2
CLR WREG
MOV.B datalength,WREG
DEC WREG, W4
DO W4, fwd
XOR.B W2, [W3++], W2
CLR W5
BTSC W2, #0
XOR.B #0x5e, W5
BTSC W2, #1
XOR.B #0xbc, W5
BTSC W2, #2
XOR.B #0x61, W5
BTSC W2, #3
XOR.B #0xc2, W5
BTSC W2, #4
XOR.B #0x9d, W5
BTSC W2, #5
XOR.B #0x23, W5
BTSC W2, #6
XOR.B #0x46, W5
BTSC W2, #7
XOR.B #0x8c, W5
NOP
MOV W5, W2
fwd:
MOV W2, WREG
MOV.B WREG,crc
#ENDASM
return crc;
}
void main()
{
unsigned int8 length;
char message[] = "Hello world.";
// Example when you have to calculate the CRC over a message in one go.
length = strlen(message);
crc = Calc_Crc8(message, length, 0);
printf("CRC-1 = %u\n", crc);
// Example when you have to calculate the CRC in multiple steps.
crc = 0; // Set the CRC start value. 1-wire protocol uses 0, other protocols often start with 0xFF.
crc = Calc_Crc8("Hello", 5, crc);
crc = Calc_Crc8(" ", 1, crc);
crc = Calc_Crc8("world.", 6, crc);
printf("CRC-2 = %u\n", crc);
}
// Generated output:
// CRC-1 = 105
// CRC-2 = 105
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Hopefully you will find this does what is needed. 
It'd actually be slightly simpler if done using int16's. 'byte wide' transfers can only be done into WREG, so I have to do double transfers to load these values and return this. However only a couple of extra instructions. |
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Manu59114
Joined: 22 Jan 2018
Posts: 34
Location: North of France
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| Posted: Tue Oct 09, 2018 8:18 am |
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Ttelmah
I want to say
| Code: |
While(true)
{
Printf("THANK YOU!!! Ttelmah for your great code!!!\r");
Printf("it's work like a charme for PCD\r");
Printf("dsPIC33EP512MU810\r");
}
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MAnu
_________________
CCS + ICD3 + PIC18F46K80 |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19830
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| Posted: Tue Oct 09, 2018 8:32 am |
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| Glad I got it right. |
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guy
Joined: 21 Oct 2005
Posts: 297
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| Posted: Thu Oct 18, 2018 9:01 pm |
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I'm guessing that a CRC lookup table is quicker?
It could be found in the DRIVERS folder, inside the file ds1993.c |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19830
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| Posted: Fri Oct 19, 2018 12:57 am |
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No, actually it's slower...
The algorithm used is very efficient, and takes about 30% less time than performing the same operation by a lookup (on the PIC24 at least). |
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