Electronic Components Datasheet Search |
|
DS1990A-F3 Datasheet(PDF) 8 Page - Dallas Semiconductor |
|
DS1990A-F3 Datasheet(HTML) 8 Page - Dallas Semiconductor |
8 / 10 page DS1990A 8 of 10 CRC ASSEMBLY LANGUAGE PROCEDURE Table 1 DO_CRC: CRC_LOOP: ZERO: PUSH ACC PUSH B PUSH ACC MOV B,#8 XRL A,CRC RRC A MOV A,CRC JNC ZERO XRL A,#18H RRC A MOV CRC,A POP ACC RR A PUSH ACC DJNZ B,CRC_LOOP POP ACC POP B POP ACC RET ; save the accumulator ; save the B register ; save bits to be shifted set shift=8bits ; ; calculate CRC ; move it to the carry ; get the last CRC value ; skip if data=0 ; update the CRC value ; ; position the new CRC ; store the new CRC ; get the remaining bits ; position the next bit ; save the remaining bits ; repeat for eight bits ; clean up the stack ; restore the B register ; restore the accumulator CRC GENERATION To validate the data transmitted from the DS1990A, the bus master may generate a CRC value from the data as it is received. This generated value is compared to the value stored in the last eight bits of the DS1990A. The bus master computes the CRC over the 8-bit family code and all 48 ID number data bits, but not over the stored CRC value itself. If the two CRC values match, the transmission is error-free. An example of how to generate the CRC using assembly language software is shown in Table 1. This assembly language code is written for the DS5000 Soft microcontroller which is compatible with the 8031/51 Microcontroller family. The procedure DO_CRC calculates the cumulative CRC of all the bytes passed to it in the accumulator. It should be noted that the variable CRC needs to be initialized to 0 before the procedure is executed. Each byte of the data is then placed in the accumulator and DO-CRC is called to update the CRC variable. After all the data has been passed to DO_CRC, the variable CRC will contain the result. The equivalent polynomial function of this software routine is: CRC = x 8 + x5 + x4 + 1 For more details, see the Book of DS19xx iButton Standards. |
Similar Part No. - DS1990A-F3 |
|
Similar Description - DS1990A-F3 |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.COM |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |