4-megabit 2.5-volt or 2.7-volt DataFlash® AT45DB041B For New Designs Use AT45DB041D Read Commands By specifying the appropriate opcode, data can be read from the main memory or from either one of the two data buffers. The DataFlash supports two categories of read modes in relation to the SCK **. The differences between the modes are in respect to the inactive state of the SCK ** as well as which clock cycle data will begin to be output. The two categories, which are comprised of four modes total, are defined as Inactive Clock Polarity Low or Inactive Clock Polarity High and SPI Mode 0 or SPI Mode 3. A separate opcode (refer to Table 5-3 on page 10 for a complete list) is used to select which category will be used for reading. Please refer to the “Detailed Bit-level Read Timing” diagrams in this datasheet for details on the clock cycle sequences for each mode. When the last bit in the main memory array has been read, the device will continue reading back at the beginning of the first page of memory. As with crossing over page boundaries, no delays will be incurred when wrapping around from the end of the array to the beginning of the array. while Reprogramming the Flash Memory Array • Continuous Read Capability through Entire Array – Ideal for Code Shadowing Applications • Low Power Dissipation – 4 mA Active Read Current Typical – 2 µA CMOS Standby Current Typical • Hardware Data Protection Feature • 5.0V-tolerant Inputs: SI, SCK, CS, RESET, and WP Pins • Commercial and Industrial Temperature Ranges • Green (Pb/Halide-free/RoHS Compliant) Package Options Pin Name Function CS Chip Select SCK Serial Clock SI Serial Input SO Serial Output WP Hardware Page Write Protect 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 or D4H is used to read data from buffer 1, and an opcode of 56H or D6H is used to read data from buffer 2. To perform a Buffer Read, the eight bits of the opcode must be followed by 15 don’t care bits, nine address bits, and eight don’t care bits. Since the buffer size is 264 bytes, nine address bits (BFA8 - BFA0) are required to specify the first byte of data to be read from the buffer. The CS pin must remain low during the loading of the opcode, the address bits, the don’t care bits, and the reading of data. When the end of a buffer is reached, the device will continue reading back at the beginning of the buffer. A low-to-high transition on the CS pin will terminate the read operation and tri-state the SO pin. Status Register Read The status register can be used to determine the device’s Ready/Busy status, the result of a Main Memory Page to Buffer Compare operation, or the device density. To read the status register, an opcode of 57H or D7H must be loaded into the device. After the last bit of the opcode is shifted in, the eight bits of the status register, starting with the MSB (bit 7), will be shifted out on the SO pin during the next eight clock cycles. The five most significant bits of the status register will contain device information, while the remaining three least-significant bits are reserved for future use and will have undefined values. After bit 0 of the status register has been shifted out, the sequence will repeat itself (as long as CS remains low and SCK is being toggled) starting again with bit 7. The data in the status register is constantly updated, so each repeating sequence will output new data.
