AT45D081中文资料(2)

AT45D081

2

Device Operation

The device operation is controlled by instructions from the host processor. The list of instructions and their associated opcodes are contained in Tables 1 and 2. A valid instruc-tion starts with the falling edge of CS followed by the appro-priate 8-bit opcode and the desired buffer or main memory address location. While the CS pin is low, toggling the SCK pin controls the loading of the opcode and the desired buffer or main memory address location through the SI (serial input) pin. All instructions, addresses, and data are transferred with the most significant bit (MSB) first.

Read

By specifying the appropriate opcode, data can be read from the main memory or from either one of the two data buffers.

MAIN MEMORY PAGE READ: A main memory read allows the user to read data directly from any one of the 4096pages in the main memory, bypassing both of the data buff-ers and leaving the contents of the buffers unchanged. To start a page read, the 8-bit opcode, 52H, is followed by 24

address bits and 32 don’t care bits. In the AT45D081, the first three address bits are reserved for larger density devices (see Notes on page 7), the next 12 address bits (PA11-PA0) specify the page address, and the next nine address bits (BA8-BA0) specify the starting byte address within the page. The 32 don’t care bits which follow the 24address bits are sent to initialize the read operation. Fol-lowing the 32 don’t care bits, additional pulses on SCK result in serial data being output on the SO (serial output)pin. The CS pin must remain low during the loading of the opcode, the address bits, and the reading of data. When the end of a page in main memory is reached during a main memory page read, the device will continue reading at the beginning of the same page. A low to high transition on the CS pin will terminate the read operation and tri-state the SO pin.

BUFFER READ: Data can be read from either one of the two buffers, using different opcodes to specify which buffer to read from. An opcode of 54H is used to read data from buffer 1, and an opcode of 56H is used to read data from

Block Diagram

FLASH MEMORY ARRAY

PAGE (264 BYTES)

BUFFER 2 (264 BYTES)

BUFFER 1 (264 BYTES)I/O INTERFACE

SCK CS RESET

V CC GND RDY/BUSY

WP

SO

SI reduces package size and active pin count. The device is optimized for use in many commercial and industrial appli-cations where high density, low pin count, low voltage, and low power are essential. Typical applications for the DataFlash are digital voice storage, image storage, and data storage. The device operates at clock frequencies up to 10 Mhz with a typical active read current consumption of 15m A.

To allow for simple in-system reprogrammability, the AT45D081 does not require high input voltages for pro-

gramming. The device operates from a single power sup-ply, 4.5V to 5.5V, for both the program and read opera-tions. The AT45D081 is enabled through the chip select pin (CS) and accessed via a three-wire interface consisting of the Serial Input (SI), Serial Output (SO), and the Serial Clock (SCK).

All programming cycles are self-timed, and no separate erase cycle is required before programming.

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