전자부품 데이터시트 검색엔진 |
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93AA86 데이터시트(PDF) 6 Page - Microchip Technology |
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93AA86 데이터시트(HTML) 6 Page - Microchip Technology |
6 / 22 page 93AA76/86 DS21130F-page 6 1996-2012 Microchip Technology Inc. 2.0 PRINCIPLES OF OPERATION When the ORG pin is connected to VCC, the x16 organization is selected. When it is connected to ground, the x8 organization is selected. Instructions, addresses and write data are clocked into the DI pin on the rising edge of the clock (CLK). The DO pin is normally held in a high-Z state except when reading data from the device, or when checking the Ready/Busy status during a programming operation. The Ready/Busy status can be verified during an erase/write operation by polling the DO pin; DO low indicates that programming is still in progress, while DO high indicates the device is ready. The DO will enter the high-impedance state on the falling edge of the CS. 2.1 Start Condition The Start bit is detected by the device if CS and DI are both high with respect to the positive edge of CLK for the first time. Before a Start condition is detected, CS, CLK and DI may change in any combination (except to that of a Start condition), without resulting in any device opera- tion (Read, Write, Erase, EWEN, EWDS, ERAL and WRAL). As soon as CS is high, the device is no longer in the Standby mode. An instruction following a Start condition will only be executed if the required amount of opcode, address and data bits for any particular instruction are clocked in. After execution of an instruction (i.e., clock in or out of the last required address or data bit) CLK and DI become “don't care” bits until a new Start condition is detected. 2.2 DI/DO It is possible to connect the Data In and Data Out pins together. However, with this configuration it is possible for a “bus conflict” to occur during the “dummy zero” that precedes the read operation, if A0 is a logic high level. Under such a condition the voltage level seen at Data Out is undefined and will depend upon the relative impedances of Data Out and the signal source driving A0. The higher the current sourcing capability of A0, the higher the voltage at the Data Out pin. 2.3 Erase/Write Enable and Disable (EWEN, EWDS) The 93AA76/86 powers up in the Erase/Write Disable (EWDS) state. All programming modes must be preceded by an Erase/Write Enable (EWEN) instruction. Once the EWEN instruction is executed, programming remains enabled until an EWDS instruction is executed or VCC is removed from the device. To protect against accidental data disturb, the EWDS instruction can be used to disable all erase/write functions and should follow all programming operations. Execution of a READ instruction is independent of both the EWEN and EWDS instructions. 2.4 Data Protection During power-up, all programming modes of operation are inhibited until VCC has reached a level greater than 1.4V. During power-down, the source data protection circuitry acts to inhibit all programming modes when VCC has fallen below 1.4V. The EWEN and EWDS commands give additional protection against accidentally programming during normal operation. After power-up, the device is automatically in the EWDS mode. Therefore, an EWEN instruction must be performed before any ERASE or WRITE instruction can be executed. 21130F.book Page 6 Wednesday, December 5, 2012 2:47 PM |
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