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M295V400T-55M3TR Datasheet(PDF) 7 Page - STMicroelectronics |
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M295V400T-55M3TR Datasheet(HTML) 7 Page - STMicroelectronics |
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7 / 34 page  DEVICE OPERATIONS See Tables 4, 5 and 6. Read. Read operations are used to output the contents of the Memory Array, the Electronic Sig- nature, the Status Register or the Block Protection Status. Both Chip Enable E and Output Enable G must be low in order to read the output of the memory. Write. Write operations are used to give Instruction Commands to the memory or to latch input data to be programmed. A write operation is initiated when Chip Enable E is Low and Write Enable W is Low with Output Enable G High. Addresses are latched on the falling edge of W or E whichever occurs last. Commands and Input Dataare latchedon the rising edge of W or E whichever occurs first. Output Disable. The data outputs are high imped- ance when the Output Enable G is High with Write Enable W High. Standby. The memory is in standby when Chip Enable E is High and the P/E.C. is idle. The power consumption is reduced to the standby level and the outputs are high impedance, independent of the Output Enable G or Write Enable W inputs. Automatic Standby. After 150ns of bus inactivity and when CMOS levels are driving the addresses, the chip automatically enters a pseudo-standby mode where consumption is reduced to the CMOS standby value, while outputs still drive the bus. Electronic Signature. Two codes identifying the manufacturer and the device can be read from the memory. The manufacturer’s code for STMi- croelectronics is 20h, the device code is D5h for the M29F400T (Top Boot) and D6h for the M29F400B (Bottom Boot). These codes allow programming equipment or applications to automatically match their interface to the characteristics of the M29F400. The Electronic Signature is output by a Read operation when the voltage applied to A9 is at VID and address inputs A1 is Low. The manufac- turer code is output when the Address input A0 is Low and the device code when this input is High. Other Address inputs are ignored. The codes are output on DQ0-DQ7. The Electronic Signature can also be read, without raising A9 to VID, by giving the memory the Instruc- tion AS. If the Byte-wide configuration is selected the codes are output on DQ0-DQ7 with DQ8-DQ14 at High impedance; if the Word-wide configuration is selected the codes are output on DQ0-DQ7 with DQ8-DQ15 at 00h. Block Protection. Each block can be separately protected against Program or Erase on program- ming equipment. Block protection provides addi- tional data security, as it disables all program or eraseoperations. Thismode is activated when both A9 and G are raised to VID and an address in the block is applied on A12-A17. The Block Protection algorithm is shown in Figure 14. Block protection is initiated on the edge of W falling to VIL. Then after a delay of 100 µs, the edge of W rising to VIH ends the protection operations. Block protection verify is achieved by bringing G, E, A0 and A6 to VIL and A1 to VIH, while W is at VIH and A9 at VID. Under these conditions, reading the data output will yield 01h if the block defined by the inputs on A12-A17 is protected. Any attempt to program or erase a pro- tected block will be ignored by the device. Block Temporary Unprotection. Any previously protected block can be temporarily unprotected in order to change stored data. The temporary unpro- tection mode is activated by bringing RP to VID. During the temporary unprotection mode the pre- viously protected blocks are unprotected. A block can be selected and data can be modified by executing the Erase or Program instruction with the RP signal held at VID. When RP is returned to VIH, all the previously protected blocks are again pro- tected. Block Unprotection. All protected blocks can be unprotected on programming equipment to allow updating of bit contents. All blocks must first be protected before the unprotection operation. Block unprotection is activated when A9, G and E are at VID and A12, A15 at VIH. The Block Unprotection algorithm is shown in Figure 15. Unprotection is initiated by the edge of W falling to VIL. After a delay of 10ms, the unprotection operation will end. Un- protection verify is achieved by bringing G and E to VIL while A0 is at VIL, A6 and A1 are at VIH and A9 remains at VID. In these conditions, reading the output data will yield 00h if the block defined by the inputs A12-A17 has been succesfully unprotected. Each block must be separately verified by giving its address in order to ensure that it has been unpro- tected. 7/34 M29F400T, M29F400B |
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