單片機(jī)外文翻譯7-單片機(jī)(存儲(chǔ)版)
【正文】 eriod. If this does not occur and the bus is left low for more than 480 ms, all ponents on the bus will be reset. TRANSACTION SEQUENCE The protocol for accessing the DS1820 via the 1–Wire port is as follows: ? Initialization ? ROM Function Command ? Memory Function Command ? Transaction/Data INITIALIZATION All transactions on the 1–Wire 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 DS1820 is on the bus and is ready to operate. For more details, see the “1–Wire Signaling” section. ROM FUNCTION COMMANDS Once 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 6): Read ROM [33h] This mand allows the bus master to read the DS1820’s 8–bit family code, unique 48–bit serial number,and 8–bit CRC. This mand can only be used if there is a single DS1820 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 64–bit ROM sequence, allows the bus master to address a specific DS1820 on a multidrop bus. Only the DS1820 that exactly matches the 64–bit ROM sequence will respond to the following memory function mand. All slaves that do not match the 64–bit 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 64–bit 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 1–Wire bus or their 64–bit ROM codes. The search ROM mand allows the bus master to use a process of elimination to identify the 64–bit ROM codes of all slave devices on the bus. 英文資料譯文 DS1820 特性： C value, is incremented, indicating that the temperature is higher than –55176。C in 176。F in 176。C to +125176。不需要外部元件； 告警搜索命令識(shí)別和尋址溫度在編定的極限之外的器件（溫度告警情況）； 在成功地執(zhí)行了 ROM 操作序列之后，可使用存貯器和控制操作，然后主機(jī)可以提供六種存貯器和控制操作命令之一。只要符合指定的定時(shí)和電壓要求， I/O將提供足夠的功率（標(biāo)題為“單總線系統(tǒng)”一節(jié)）。 向 DS1820 供電的另外一種方法是通過(guò)使用連接到 VDD 引腳的外部電源，如圖 3 所示這種方法的優(yōu)點(diǎn)是在 I/O 線上不要求強(qiáng)的上拉。如果是寄生供電， DS1820 將在單線總線上送回“ 0”；如果由 VDD 引腳供電，它將送回 1。時(shí)鐘再次使計(jì)數(shù)器計(jì)值至它達(dá)到零。 DS1820 可以以 ℃ 的增量值，在 ℃ 至 +125℃ 的范圍內(nèi)測(cè)量溫度。所需的最后一個(gè)數(shù)值是在該溫度處每一攝氏度的計(jì)數(shù)個(gè)數(shù)（ COUNT_PER_C）。 存在脈沖（ presence pulse） 使總線主機(jī)知道 DS1820 在總線上并已準(zhǔn)備好工作。 ROM 操作命令 一旦總線主機(jī)檢測(cè)到從屬器件的存在，它便可以發(fā)出器件 ROM 操作命令之一。后繼以 64 位的 ROM 數(shù)據(jù)序列，允許總線主機(jī)對(duì)多點(diǎn)總線上特定的 DS1820尋址。搜索 ROM 命令允許總線主機(jī)使用一種“消去”（ elimination）處理來(lái)識(shí)別總線上所有從片的 64 位 ROM 編碼。 (“跳過(guò)” ROM ) [CCh] 在單點(diǎn)總線系統(tǒng)中，此命令通過(guò)允許總線主機(jī)不提供 64 位 ROM 編碼而訪問(wèn)存儲(chǔ)器操作來(lái)節(jié)省時(shí)間。此命令只能在總線上僅有一個(gè) DS1820 的情況下可以使用。 ROM 操作命令 單線總線要求近似等于 5k的上拉電阻。首先，讀溫度，并從讀得的值截 去 ℃ 位 (最低有效位 )。因此，為了獲得所需的分辯率，計(jì)數(shù)器的數(shù)值以及在給定溫度處每一攝氏度的計(jì)數(shù)個(gè)數(shù)（鈄率累加器的值）二者都必須知道。溫度測(cè)量電路的方框圖見(jiàn)圖 4 所示。注意只要外部電源處于工作狀態(tài)， GND（地引）腳不可懸空。 有兩種方法確保 DS1820 在其有效變換期內(nèi)得到足夠的電源電流。如果不對(duì) DS1820 施加告警搜索命令，這些寄存器可用作通用用戶存儲(chǔ)器使用存儲(chǔ)器，操作命令可以寫 TH 和 TL 對(duì)這些寄存器的讀訪問(wèn)。作為另一種可供選擇的方法， DS1820也可以用外部
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