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M29W800AT Datasheet(PDF) 7 Page - STMicroelectronics |
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M29W800AT Datasheet(HTML) 7 Page - STMicroelectronics |
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7 / 33 page  7/33 M29W800AT, M29W800AB DEVICE OPERATIONS See Tables 5, 6 and 7. 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 mem- ory. A new operation is initiated either on the fol- lowing edge of Chip Enable E or on any address transition with E at VIL. Write. Write operations are used to give Instruc- tion Commands to the memory or to latch input data to be programmed. A write operation is initi- ated 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 Data are latched on the rising edge of W or E whichever oc- curs first. Output Disable. The data outputs are high im- pedance when the Output Enable G is High with Write Enable W High. Stan-by. The memory is in stan-by when Chip Enable E is High and the P/E.C. is idle. The power consumption is reduced to the stan-by level and the outputs are high impedance, independent of the Output Enable G or Write Enable W inputs. Automatic Stan-by. After 150ns of bus inactivity (no address transition, CE = VIL) and when CMOS levels are driving the addresses, the chip automat- ically enters a pseudo-stan-by mode where con- sumption is reduced to the CMOS stan-by value, while outputs still drive the bus (if G = VIL). Electronic Signature. Two codes identifying the manufacturer and the device can be read from the memory. The manufacturer’s code for STMicro- electronics is 20h, the device code is D7h for the M29W800AT (Top Boot) and 5Bh for the M29W800AB (Bottom Boot). These codes allow programming equipment or applications to auto- matically match their interface to the characteris- tics of the M29W800A. The Electronic Signature is output by a Read operation when the voltage ap- plied to A9 is at VID and address inputs A1 is Low. The manufacturer code is output when the Ad- dress input A0 is Low and the device code when this input is High. Other Address inputs are ig- nored. The codes are output on DQ0-DQ7. The Electronic Signature can also be read, without raising A9 to VID, by giving the memory the In- struction AS. If the Byte-wide configuration is se- lected 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 erase operations. This mode is activated when both A9 and G are raised to VID and an address in the block is applied on A12-A18. Block protection is initiated on the edge of W falling to VIL. Then af- ter 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-A18 is protected. Any attempt to program or erase a protected block will be ignored by the de- vice. Block Temporary Unprotection. Any previously protected block can be temporarily unprotected in order to change stored data. The temporary un- protection 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 exe- cuting 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. Unprotection is initiated by the edge of W falling to VIL. After a delay of 10ms, the unprotection operation will end. Unpro- tection 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-A18 has been successfully unprotect- ed. Each block must be separately verified by giv- ing its address in order to ensure that it has been unprotected. |
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