Netronix CTU-M Series Technical Data Sheet page 11

NETRONIX
Family code
1 byte
ID1...5 – unique ID number of transponder
CRC_DAL- check sum of data send
The format conforms 1-WIRE Dallas (e.g.. DS1990A). It means, that described
module could be used as a replacement of DS1990A drop.
During operation, a module tries to read-out transponder periodically. If it fails (no
successful read-out), module does not response for pulses sent from 1-WIRE master
unit. Bus does not "see" the module, which corresponds with lack of reader applying, it
means applying the DS1990A drop to drop reader. If module reads out the
transponder, the module starts to send data via 1-WIRE bus.
Calculate the CRC value
According to DS1990A specification C value is calculated from equation
x^8+x^5+x^4+1 with initial value equal to 0x00. The CRC is calculated on basis of all
frame bytes excluding the last one.
An example of CRC value calculation procedure written in C language
unsigned char CalcCRCDallas(unsigned char *SourceAdr)
{
unsigned char i,k,In,CRC=0;
for(i=0;i<7;i++)
{
In=*SourceAdr;
for(k=0;k<8;k++)
{
if((In^CRC)&1) CRC=((CRC^0x18)>>1)|0x80;
else CRC=CRC>>1;
In>>=1;
}
SourceAdr++;
}
return(CRC);
}
where *SourceAdr is beginning flag of data buffer
NETRONIX
ID1...ID5
5 bytes
CTU-Mxx
Address CRC
1 byte 1 bytet
.
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