What is ROM? Read-Only Memory ROM is a type of computer memory which, generally speaking, is only programmed once or very occasionally and then gets read from the rest of the time. This makes it ideal for things like firmware which need to be "remembered" by the computer, but never actually change. This was memory made up of discrete semiconductor diodes placed on a specially organized PCB. This gave way to Mask ROM with the advent of integrated circuits. Mask ROM had to be programmed by the manufacturer and was thereafter not alterable.
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Low-voltage and Standard-voltage Operation — 5. The device is optimized for use in many industrial and commercial applications where low-power and low-voltage operation are essential. In addition, the entire family is available in 5.
This is a stress rating only and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. This pin is open-drain driven and may be wire-ORed with any number of other open-drain or open collector devices. When the pins are hardwired, as many as four K devices may be addressed on a single bus system device addressing is discussed in detail under the Device Addressing section.
When the pins are not hardwired, the default A1 and A0 are zero. Random word addressing requires a bit data word address. Test conditions are listed in Note 2. STA tSU. STA tHD. DAT tSU. Data changes during SCL high periods will indicate a start or stop condition as defined below. The device address word consists of a mandatory one, zero sequence for the first five most significant bits as shown.
The K uses the two device address bits A1, A0 to allow as many as four devices on the same bus. These bits must compare to their corresponding hardwired input pins. The A1 and A0 pins use an internal proprietary circuit that biases them to a logic low condition if the pins are allowed to float. A read operation is initiated if this bit is high and a write operation is initiated if this bit is low. If a compare is not made, the device will return to a standby state.
This involves sending a start condition followed by the device address word. Only if the internal write cycle has completed will the EEPROM respond with a zero, allowing the read or write sequence to continue. There are three read operations: current address read, random address read and sequential read.
This address stays valid between operations as long as the chip power is maintained. The microcontroller does not respond with an input zero but does generate a following stop condition refer to Figure 4. Once the device address word and data word address are clocked in and acknowledged by the EEPROM, the microcontroller must generate another start condition. The microcontroller does not respond with a zero but does generate a following stop condition refer to Figure 5.
After the microcontroller receives a data word, it responds with an acknowledge. As long as the EEPROM receives an acknowledge, it will continue to increment the data word address and serially clock out sequential data words.
The sequential read operation is terminated when the microcontroller does not respond with a zero but does generate a following stop condition refer to Figure 6. The addressing device, such as a microcontroller, then must terminate the write sequence with a stop condition.
A page write is initiated the same way as a byte write, but the microcontroller does not send a stop condition after the first data word is clocked in. Instead, after the EEPROM acknowledges receipt of the first data word, the microcontroller can transmit up to more data words.
The microcontroller must terminate the page write sequence with a stop condition refer to Figure 3. The data word address lower 7 bits are internally incremented following the receipt of each data word. The higher data word address bits are not incremented, retaining the memory page row location. When the word address, internally generated, reaches the page boundary, the following byte is placed at the beginning of the same page.
Device Address Figure 2. Byte Write Figure 3. Page Write Figure 4. Random Read Figure 6. A ISB max? Cheyenne Mtn. Atmel Corporation The Company assumes no responsibility for any errors which may appear in this document, reserves the right to change devices or specifications detailed herein at any time without notice, and does not make any commitment to update the information contained herein. No licenses to patents or other intellectual property of Atmel are granted by the Company in connection with the sale of Atmel products, expressly or by implication.
Marks bearing? Printed on recycled paper.
Reading and Writing Serial EEPROMs
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