DS1990 DALLAS [Dallas Semiconductor], DS1990 Datasheet
DS1990
Available stocks
Related parts for DS1990
DS1990 Summary of contents
Page 1
... DS1990A SPECIAL FEATURES § Upgrade of DS1990 allows multiple Serial Number iButtons to reside on a common bus § Unique 48–bit serial number § Low-cost electronic key for access control § 8-bit CRC for checking data integrity § Can be read in less than 5 ms § ...
Page 2
... The 1-Wire bus is a system which has a single bus master system and one or more slaves. In all instances, the DS1990A 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 type and timing) ...
Page 3
... DS1990A MEMORY MAP Figure 1 8-Bit CRC Code MSB LSB MSB DS1990A EQUIVALENT CIRCUIT Figure 2 BUS MASTER CIRCUIT Figure 3 48-Bit Serial Number LSB MSB To data connection of DS1990A DS1990A 8-Bit Family Code (01h) LSB To data connection of DS1990A ...
Page 4
... The presence pulse lets the bus master know that the DS1990A is on the bus and is ready to operate. For more details, see the “1-Wire Signaling” section. ...
Page 5
... ROM FUNCTIONS FLOW CHART Figure DS1990A ...
Page 6
... DS1990A. During write time slots, the delay circuit determines when the DS1990A will sample the data line. For a read data time slot “0” transmitted, the delay circuit determines how long the DS1990A will hold the data line low overriding the 1 generated by the master. If the data bit is a “ ...
Page 7
... DS1990A < 120 s SLOT < LOW1 < REC < t < 120 s LOW0 SLOT < REC < 120 s SLOT < LOWR 0 t < RELEASE < REC RDV DS1990A ...
Page 8
... 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. ...
Page 9
... PDH t 60 PDL =2.8V to 6.0V; -40°C to +85°C) MAX UNITS NOTES V +0 +0.8 V 0 (TA = 25°C) MAX UNITS NOTES 800 pF =2.8V to 6.0V; -40°C to +85°C) MAX UNITS NOTES 120 120 240 s DS1990A 1 1 ...
Page 10
... RSTL otherwise, it could mask or conceal interrupt pulses if this device is used in parallel with a DS1994. and a maximum time slot of 120 after power has been applied the parasite capacitance will not affect supply. CC DS1990A ...