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DS2411 Datasheet(PDF) 8 Page - Maxim Integrated Products |
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DS2411 Datasheet(HTML) 8 Page - Maxim Integrated Products |
8 / 12 page DS2411 8 of 12 1-WIRE SIGNALING The DS2411 requires strict protocols to ensure data integrity. The protocol consists of four types of signaling on one line: Reset Sequence with Reset Pulse and Presence Pulse, Write 0, Write 1, and Read Data. Except for the presence pulse the bus master initiates all these signals. The DS2411 can communicate at two different speeds: standard speed and Overdrive speed. If not explicitly set into the Overdrive mode, the DS2411 will communicate at standard speed. While in Overdrive Mode the fast timing applies to all waveforms. To get from idle to active, the voltage on the 1-Wire line needs to fall from VPUP below the threshold VTL. To get from active to idle, the voltage needs to rise from VILMAX past the threshold VTH. The voltage VILMAX is relevant for the DS2411 when determining a logical level, but not for triggering any events. The initialization sequence required to begin any communication with the DS2411 is shown in Figure 6. A Reset Pulse followed by a Presence Pulse indicates the DS2411 is ready to receive data, given the correct ROM and memory function command. In a mixed population network, the reset low time tRSTL needs to be long enough for the slowest 1-Wire slave device to recognize it as a reset pulse. If the bus master uses slew-rate control on the falling edge, it must pull down the line for tRSTL + tF to compensate for the edge. A tRSTL duration of 480µs or longer will exit the Overdrive Mode returning the device to standard speed. If the DS2411 is in Overdrive Mode and tRSTL is no longer than 80µs, the device will remain in Overdrive Mode. After the bus master has released the line it goes into receive mode (RX). Now, the 1-Wire bus is pulled to VPUP via the pullup resistor or, in case of a DS2480B driver, by active circuitry. When the threshold VTH is crossed, the DS2411 waits for tPDH and then transmits a Presence Pulse by pulling the line low for tPDL. To detect a presence pulse, the master must test the logical state of the 1-Wire line at tMSP. The tRSTH window must be at least the sum of tPDHMAX, tPDLMAX, and tRECMIN. Immediately after tRSTH is expired, the DS2411 is ready for data communication. In a mixed population network, tRSTH should be extended to minimum 480µs at standard speed and 48µs at Overdrive speed to accommodate other 1- Wire devices. Read/Write Time Slots Data communication with the DS2411 takes place in time slots that carry a single bit each. Write time slots transport data from bus master to slave. Read time-slots transfer data from slave to master. The definitions of the write and read time slots are illustrated in Figure 7. All communication begins with the master pulling the data line low. As the voltage on the 1-Wire line falls below the threshold VTL, the DS2411 starts its internal timing generator that determines when the data line will be sampled during a write time slot and how long data will be valid during a read time slot. Master to Slave For a write-one time slot, the voltage on the data line must have crossed the VTHMAX threshold after the write-one low time tW1LMAX is expired. For a write-zero time slot, the voltage on the data line must stay below the VTHMIN threshold until the write-zero low time tW0LMIN is expired. For most reliable communication the voltage on the data line should not exceed VILMAX during the entire tW0L window. After the VTHMAX threshold has been crossed, the DS2411 needs a recovery time tREC before it is ready for the next time slot. |
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