基于單片機(jī)ds18b20的數(shù)字溫度計(jì)中英文獻(xiàn)翻譯-wenkub.com
2025-06-22 14:07 本頁面
【正文】 .The idle state for the 1Wire bus is high. If for any reason a transaction needs to be suspended, the bus MUST be left in the idle state if the transaction is to resume. Infinite recovery time can occur between bits so long as the 1Wire bus is in the inactive (high) state during the recovery period. If this does not occur and the bus is left low for more than 480 s, all ponents on the bus will be reset.HARDWARE CONFIGURATION TRANSACTION SEQUENCEThe protocol for accessing the DS18B20 via the 1Wire port is as follows:_ Initialization_ ROM Function Command_ Memory Function Command_ Transaction/DataINITIALIZATIONAll transactions on the 1Wire bus begin with an initialization sequence. The initialization sequence consists of a reset pulse transmitted by the bus master followed by presence pulse(s) transmitted by the slave(s). The presence pulse lets the bus master know that the DS18B20 is on the bus and is ready to operate. For more details, see the “1Wire Signaling” section.ROM FUNCTION COMMANDSOnce the bus master has detected a presence, it can issue one of the five ROM function mands. All ROM function mands are 8 bits long. A list of these mands follows (refer to flowchart in Figure 5)Read ROM [33h]This mand allows the bus master to read the DS18B20’s 8bit family code, unique 48bit serial number, and 8bit CRC. This mand can only be used if there is a single DS18B20 on the bus. If more than one slave is present on the bus, a data collision will occur when all slaves try to transmit at the same time (open drain will produce a wired AND result).Match ROM [55h]The match ROM mand, followed by a 64bit ROM sequence, allows the bus master to address a specific DS18B20 on a multidrop bus. Only the DS18B20 that exactly matches the 64bit ROM sequence will respond to the following memory function mand. All slaves that do not match the 64bit ROM sequence will wait for a reset pulse. This mand can be used with a single or multiple devices on the bus.Skip ROM [CCh]This mand can save time in a single drop bus system by allowing the bus master to access the memory functions without providing the 64bit ROM code. If more than one slave is present on the bus and a Read mand is issued following the Skip ROM mand, data collision will occur on the bus as multiple slaves transmit simultaneously (open drain pulldowns will produce a wired AND result).Search ROM [F0h]When a system is initially brought up, the bus master might not know the number of devices on the 1Wire bus or their 64bit ROM codes. The search ROM mand allows the bus master to use a process of elimination to identify the 64bit ROM codes of all slave devices on the bus.Alarm Search [ECh]The flowchart of this mand is identical to the Search ROM mand. However, the DS18B20 will respond to this mand only if an alarm condition has been encountered at the last temperature measurement. An alarm condition is defined as a temperature higher than TH or lower than TL. The alarm condition remains set as long as the DS18B20 is powered up, or unt
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