DS1904 Maxim, DS1904 Datasheet
DS1904
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DS1904 Summary of contents
Page 1
... DESCRIPTION The DS1904 RTC iButton is a rugged real-time clock module that can be accessed with minimal hardware. Data is transferred serially via the 1-Wire protocol, which requires only a single data lead and a ground return. The DS1904 contains a unique 64-bit factory-lasered ROM and a real-time clock/calendar 1-Wire and iButton are registered trademarks of Maxim Integrated Products, Inc. ...
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... LITHIUM 64-BIT LASERED ROM Each DS1904 contains a unique ROM code that is 64 bits long. The first eight bits are a 1-Wire family code. The next 48 bits are a unique serial number. The last eight bits are a CRC of the first 56 bits (see Figure 3). The 1-Wire CRC is generated using a polynomial generator consisting of a shift register and XOR gates as shown in Figure 4. The polynomial is X Maxim 1-Wire Cyclic Redundancy Check is available in Application Note 937: Book of iButton® ...
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... HIERARCHICAL STRUCTURE FOR 1-WIRE PROTOCOL Figure 2 Bus Master Command Level 1-Wire ROM Function Commands (see Figure 7) DS1904 specific Function Commands (see Figure 5) 64-BIT LASERED ROM Figure 3 MSB 8-Bit CRC Code MSB LSB 1-WIRE CRC GENERATOR Figure 4 1ST 2ND 3RD STAGE STAGE ...
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... The “Clock Function Flow Chart” (Figure 5) describes the protocols necessary for accessing the real-time clock. With only four bytes of real-time clock and one control byte the DS1904 does not provide random access. Reading and writing always starts with the device control byte followed by the least significant byte of the time data ...
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... N Write Clock ? Y Bus Master TX Device Control Byte Bus Master TX LS Byte (7:0) Bus Master TX next Byte (15:8) Bus Master TX next Byte (23:16) Bus Master TX MS Byte (31:24) N Bus Master TX Reset ? Y DS1904 copies R/W Buffer to RTC Counter DS1904 TX Presence Pulse Bus Master TX Reset ? Y DS1904 ...
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... The 1-Wire bus is a system, which has a single bus master and one or more slaves. In all instances the DS1904 is a slave device. The bus master is typically a microcontroller. The discussion of this bus system is broken down into three topics: hardware configuration, transaction sequence, and 1-Wire signaling (signal types and timing) ...
Page 7
... If this does not occur and the bus is left low for more than 120 µs, one or more of the devices on the bus may be reset. Since the DS1904 gets all its energy for operation through its V an extended time period ...
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... Command Command ? ? Y DS1904 TX Bit 0 Master TX Bit 0 DS1904 TX Bit 0 Master TX Bit Bit 0 Bit 0 Match ? Match ? Y DS1904 TX Bit 1 Master TX Bit 1 DS1904 TX Bit 1 Master TX Bit Bit 1 Bit 1 Match ? Match ? Y DS1904 TX Bit 63 DS1904 TX Bit 63 Master TX Bit 63 Master TX Bit Bit 63 Bit 63 Match ? Match ? ...
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... For a read data time slot “0” transmitted, the delay circuit deter- mines how long the DS1904 will hold the data line low. If the data bit is a “1”, the DS1904 will not hold the data line low at all. , minimum 480 µ ...
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... REC t SLOT Master Sampling Window LOWR t RDV 60 µs ≤ t < 120 µs SLOT 1 µs ≤ t < 15 µs LOWR 0 ≤ t < 45 µs RELEASE REC t REC t REC t RELEASE ∞ 1 µs ≤ t < REC µs RDV t < 1 µs SU DS1904 ...
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... LOW0 t 1 LOWR t exactly 15 RDV RELEASE REC t 480 RSTH t 480 RSTL t 15 PDH t 60 PDL - DS1904 MAX UNITS NOTES µA 3 MAX UNITS NOTES MAX UNITS NOTES 120 µs 15 µs 120 µ ...
Page 12
... Guaranteed by design; not production tested. 9. This specification applies if the 1-Wire is idle (high or low). Communication on the 1-Wire may adversely affect the accuracy of the device. For highest accuracy, connect the DS1904 to a separate 1-Wire port and limit the access to the minimum acceptable by the application. ...
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... © 2011 Maxim Integrated Products DESCRIPTION from the DC PUP Maxim is a registered trademark of Maxim Integrated Products, Inc. DS1904 PAGES CHANGED — 11 ...