DS2437S-3/T&R Maxim Integrated Products, DS2437S-3/T&R Datasheet - Page 10

IC MONITOR SMART BATTERY 16-SSOP

DS2437S-3/T&R

Manufacturer Part Number
DS2437S-3/T&R
Description
IC MONITOR SMART BATTERY 16-SSOP
Manufacturer
Maxim Integrated Products
Datasheet

Specifications of DS2437S-3/T&R

Function
Battery Monitor
Battery Type
Smart Batteries
Voltage - Supply
2.7 V ~ 10 V
Operating Temperature
-40°C ~ 85°C
Mounting Type
Surface Mount
Package / Case
16-SSOP
Lead Free Status / RoHS Status
Contains lead / RoHS non-compliant
DS2437
64-BIT LASERED ROM
Each DS2437 contains a unique ROM code that is 64 bits long. The first 8 bits are a 1-Wire family code
(DS2437 code is 1Eh). The next 48 bits are a unique serial number. The last 8 bits are a CRC of the first
56 bits. (See Figure 3.) The 64-bit ROM and ROM Function Control section allow the DS2437 to operate
as a 1-Wire device and follow the 1-Wire protocol detailed in the section “1-Wire Bus System.” The
functions required to control sections of the DS2437 are not accessible until the ROM function protocol
has been satisfied. This protocol is described in the ROM function protocol flow chart (Figure 4). The
1-Wire bus master must first provide one of four ROM function commands: 1) Read ROM, 2) Match
ROM, 3) Search ROM, or 4) Skip ROM. After a ROM function sequence has been successfully executed,
the functions specific to the DS2437 are accessible and the bus master may then provide and one of the
six memory and control function commands.
64-Bit Lasered ROM Figure 3
CRC Generation
The DS2437 has an 8-bit CRC stored in the most significant byte of the 64-bit ROM. The bus master can
compute a CRC value from the first 56 bits of the 64-bit ROM and compare it to the value stored within
the DS2437 to determine if the ROM data has been received error-free by the bus master. The equivalent
polynomial function of this CRC is:
8
5
4
CRC = X
+ X
+ X
+1
The DS2437 also generates an 8-bit CRC value using the same polynomial function shown above and
provides this value to the bus master to validate the transfer of data bytes. In each case where a CRC is
used for data transfer validation, the bus master must calculate a CRC value using the polynomial
function given above and compare the calculated value to either the 8-bit CRC value stored in the 64-bit
ROM portion of the DS2437 (for ROM reads) or the 8-bit CRC value computed within the DS2437
th
(which is read as a 9
byte when a scratchpad is read). The comparison of CRC values and decision to
continue with an operation are determined entirely by the bus master. There is no circuitry inside the
DS2437 that prevents a command sequence from proceeding if the CRC stored in or calculated by the
DS2437 does not match the value generated by the bus master. Proper use of the CRC as outlined in the
flowchart of Figure 6 can result in a communication channel with a very high level of integrity.
The 1-Wire CRC can be generated using a polynomial generator consisting of a shift register and XOR
gates as shown in Figure 4. Additional information about the Dallas 1-Wire Cyclic Redundancy Check is
available in Application Note 27 entitled “Understanding and Using Cyclic Redundancy Checks with
Dallas Semiconductor Touch Memory Products.”
The shift register bits are initialized to 0. Then starting with the least significant bit of the family code,
th
1 bit at a time is shifted in. After the 8
bit of the family code has been entered, then the serial number is
th
entered. After the 48
bit of the serial number has been entered, the shift register contains the CRC
value.
10 of 31

Related parts for DS2437S-3/T&R