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93C46 Folha de dados(PDF) 4 Page - Microchip Technology |
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93C46 Folha de dados(HTML) 4 Page - Microchip Technology |
4 / 12 page 93C46B DS21172D-page 4 Preliminary © 1997 Microchip Technology Inc. 3.0 FUNCTIONAL DESCRIPTION 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-Z state on the falling edge of the CS. 3.1 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 oper- ation (ERASE, ERAL, EWDS, EWEN, READ, WRITE, 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 opcodes, addresses, and data bits for any particular instruction is 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. 3.2 Data In (DI) and Data Out (DO) It is possible to connect the Data In (DI)and Data Out (DO) pins together. However, with this configuration, if A0 is a logic-high level, it is possible for a “bus conflict” to occur during the “dummy zero” that precedes the READ operation. Under such a condition, the voltage level seen at DO is undefined and will depend upon the relative impedances of DO and the signal source driv- ing A0. The higher the current sourcing capability of A0, the higher the voltage at the DO pin. 3.3 Data Protection During power-up, all programming modes of operation are inhibited until Vcc has reached a level greater than 3.8V. During power-down, the source data protection circuitry acts to inhibit all programming modes when Vcc has fallen below 3.8V at nominal conditions. The ERASE/SRITE Disable (EWDS) and ERASE/ WRITE Enable (EWEN) commands give additional pro- tection against accidental 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. FIGURE 3-1: SYNCHRONOUS DATA TIMING CS VIH VIL VIH VIL VIH VIL VOH VOL VOH VOL CLK DI DO (READ) DO (PROGRAM) TCSS TDIS TCKH TCKL TDIH TPD TCSH TPD TCZ STATUS VALID TSV TCZ Note: AC test conditions: VIL = 0.4V, VIH = 2.4V |
Nº de peça semelhante - 93C46 |
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Descrição semelhante - 93C46 |
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