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25LC010A Datasheet(PDF) 6 Page - Microchip Technology |
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25LC010A Datasheet(HTML) 6 Page - Microchip Technology |
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6 / 38 page  25AA010A/25LC010A DS21832H-page 6 2003-2012 Microchip Technology Inc. 2.0 FUNCTIONAL DESCRIPTION 2.1 Principles of Operation The 25XX010A is a 128 byte Serial EEPROM designed to interface directly with the Serial Peripheral Interface (SPI) port of many of today’s popular microcontroller families, including Microchip’s PIC® microcontrollers. It may also interface with microcontrollers that do not have a built-in SPI port by using discrete I/O lines programmed properly in firmware to match the SPI protocol. The 25XX010A contains an 8-bit instruction register. The device is accessed via the SI pin, with data being clocked in on the rising edge of SCK. The CS pin must be low and the HOLD pin must be high for the entire operation. Table 2-1 contains a list of the possible instruction bytes and format for device operation. All instructions, addresses, and data are transferred MSb first, LSb last. Data (SI) is sampled on the first rising edge of SCK after CS goes low. If the clock line is shared with other peripheral devices on the SPI bus, the user can assert the HOLD input and place the 25XX010A in ‘HOLD’ mode. After releasing the HOLD pin, operation will resume from the point when the HOLD was asserted. 2.2 Read Sequence The device is selected by pulling CS low. The 8-bit READ instruction is transmitted to the 25XX010A followed by an 8-bit address. See Figure 2-1 for more details. After the correct READ instruction and address are sent, the data stored in the memory at the selected address is shifted out on the SO pin. Data stored in the memory at the next address can be read sequentially by continuing to provide clock pulses to the slave. The internal Address Pointer automatically increments to the next higher address after each byte of data is shifted out. When the highest address is reached (7Fh), the address counter rolls over to address 00h allowing the read cycle to be continued indefinitely. The read operation is terminated by raising the CS pin (Figure 2-1). 2.3 Write Sequence Prior to any attempt to write data to the 25XX010A, the write enable latch must be set by issuing the WREN instruction (Figure 2-4). This is done by setting CS low and then clocking out the proper instruction into the 25XX010A. After all eight bits of the instruction are transmitted, CS must be driven high to set the write enable latch. If the write operation is initiated immedi- ately after the WREN instruction without CS driven high, data will not be written to the array since the write enable latch was not properly set. After setting the write enable latch, the user may proceed by driving CS low, issuing a WRITE instruction, followed by the remainder of the address, and then the data to be written. Up to 16 bytes of data can be sent to the device before a write cycle is necessary. The only restriction is that all of the bytes must reside in the same page. Additionally, a page address begins with XXXX 0000 and ends with XXXX 1111. If the internal address counter reaches XXXX 1111 and clock signals continue to be applied to the chip, the address counter will roll back to the first address of the page and over- write any data that previously existed in those locations. For the data to be actually written to the array, the CS must be brought high after the Least Significant bit (D0) of the nth data byte has been clocked in. If CS is driven high at any other time, the write operation will not be completed. Refer to Figure 2-2 and Figure 2-3 for more detailed illustrations on the byte write sequence and the page write sequence, respectively. While the write is in progress, the STATUS register may be read to check the status of the WIP, WEL, BP1 and BP0 bits (Figure 2-6). Attempting to read a memory array location will not be possible during a write cycle. Polling the WIP bit in the STATUS register is recommended in order to determine if a write cycle is in progress. When the write cycle is completed, the write enable latch is reset. Note: Page write operations are limited to writing bytes within a single physical page, regardless of the number of bytes actually being written. Physical page boundaries start at addresses that are integer multiples of the page buffer size (or ‘page size’) and, end at addresses that are integer multiples of page size – 1. If a Page Write command attempts to write across a physical page boundary, the result is that the data wraps around to the beginning of the current page (overwriting data previously stored there), instead of being written to the next page as might be expected. It is therefore necessary for the application software to prevent page write operations that would attempt to cross a page boundary. |
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