Post by thread:CRC program for PIC 16CXX

Thanks for all those who responded. In return, here I present a debugged and tested CRC routine for y'all. Program to calculate CRC-16 on a 16Cxx. The resulting CRC value is identical to that calculated by common archive programs, such as ZOO. Fast table-based CRC calculators for this polynomial are available as C source. Note that the resulting CRC has its bits reversed in comparison to the sources posted yesterday; this is to be compatible with ZOO and ARC and others (most of all, with the CRC16 routine in my standard library), and also is compatible with serial transmission if the least significant bit is sent first. ----- C source -------------------------------------------------------- unsigned CRC; unsigned crc_16(char c) { int i,j; for(i=0;i!=8;c>>=1,i++) { j=(c^CRC)&1; CRC>>=1; if(j) CRC^=0xa001; } return CRC; } ----- 16CXX source ---------------------------------------------------- Temp = 0x20 Count = 0x21 CRC_High = 0x22 CRC_Low = 0x23 loop macro reg,label decfsz reg goto label endm movlw "h" call CalcCRC movlw "e" call CalcCRC movlw "l" call CalcCRC movlw "l" call CalcCRC movlw "o" call CalcCRC Halt goto Halt ; result=0x34d2 (you can check that with ZOO) ----- CRC subroutine -------------------------------------------------- CalcCRC movwf Temp ; about 125 cycles on average movlw 8 movwf Count CRC_Loop movf CRC_Low,w xorwf Temp,w clrc rrf CRC_High rrf CRC_Low andlw 1 bz CRC_Skip movlw 0xa0 xorwf CRC_High movlw 0x01 xorwf CRC_Low CRC_Skip rrf Temp loop Count,CRC_Loop return ----------------------------------------------------------------------- Share And Enjoy. Frank "It's justice, Jim, but not as we know it." ------------------------------------------------------------------------ Frank A. Vorstenbosch +31-(70)-355 5241 spam_OUTfalstaffTakeThisOuTxs4all.nl