Maxim Integrated DS4830A Optical Microcontroller - Manual (Page 239)

DS4830A User’s Guide
239
SECTION 26 – MISCELLANEOUS
26.1 – Overview
Miscellaneous features of DS4830A are
• CRC8
• Software interrupts
• General-purpose registers.
26.2 – CRC8
DS4830A has an built-in hardware CRC8. The registers used for CRC8 are CRC8IN and CRC8OUT. They are
defined in Module 1. SMBus 2.0 specification is followed for CRC algorithm (CRC polynomial is x
8
+x
2
+x+1).
26.2.1 – CRC Data In (CRC8IN)
Bit 7 6 5 4 3 2 1 0
Name CRC8IN_7 CRC8IN_6 CRC8IN_5 CRC8IN_4 CRC8IN_3 CRC8IN_2 CRC8IN_1 CRC8IN_0
Reset 0 0 0 0 0 0 0 0
Access rw rw rw rw rw rw rw rw
BIT NAME DESCRIPTION
7:0 CRC8IN[7:0] CRC Data in. The user program writes data to this register for which CRC8 should be
applied to.
26.2.2 – CRC Data Out (CRC8OUT)
Bit 7 6 5 4 3 2 1 0
Name CRC8OUT_7 CRC8OUT_6 CRC8OUT_5 CRC8OUT_4 CRC8OUT_3 CRC8OUT_2 CRC8OUT_1 CRC8OUT_0
Reset 0 0 0 0 0 0 0 0
Access rw rw rw rw rw rw rw rw
BIT NAME DESCRIPTION
7:0 CRC8OUT[7:0] CRC Data out. The user program reads CRC8 result from this register for all the
data that was written to CRC8IN.
Note: This register has to be cleared to 0x00 by software before starting a CRC8
calculation.
26.2.3 – Example
unsigned char Calculate_CRC8(unsigned char* data, int length)
{
unsigned int i = 0;
unsigned char CRC_result;
CRC8OUT = 0x00;
for( ; i<length ; i++)
{
CRC8IN = data[i];
//Incrementing i in the loop takes a cycle atleast. So CRC should have been completed in this time.
}
CRC_result = CRC8OUT;
return CRC_result;
}
26.3 – Software Interrupts
The DS4830A has four software interrupts that the application program can use to generate interrupts for general-
purpose application requirements. The user can generate an interrupt by setting a bit in the USER_INT[3:0]. The
USER_INT[7:4] are single cycle read/write bits which can be used in the time critical interrupts.