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FM24C04A Arkusz danych(PDF) 4 Page - Ramtron International Corporation |
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FM24C04A Arkusz danych(HTML) 4 Page - Ramtron International Corporation |
4 / 12 page FM24C04A Rev. 3.0 Mar. 2005 4 of 12 Figure 3. Data Transfer Protocol Stop Condition A Stop condition is indicated when the bus master drives SDA from low to high while the SCL signal is high. All operations must end with a Stop condition. If an operation is pending when a stop is asserted, the operation will be aborted. The master must have control of SDA (not a memory read) in order to assert a Stop condition. Start Condition A Start condition is indicated when the bus master drives SDA from high to low while the SCL signal is high. All read and write transactions begin with a Start condition. An operation in progress can be aborted by asserting a Start condition at any time. Aborting an operation using the Start condition will ready the FM24C04A for a new operation. If during operation the power supply drops below the specified VDD minimum, the system should issue a Start condition prior to performing another operation. Data/Address Transfer All data transfers (including addresses) take place while the SCL signal is high. Except under the two conditions described above, the SDA signal should not change state while SCL is high. Acknowledge The Acknowledge takes place after the 8 th data bit has been transferred in any transaction. During this state the transmitter should release the SDA bus to allow the receiver to drive it. The receiver drives the SDA signal low to acknowledge receipt of the byte. If the receiver does not drive SDA low, the condition is a No-Acknowledge and the operation is aborted. The receiver could fail to acknowledge for two distinct reasons. First, if a byte transfer fails, the No- Acknowledge ends the current operation so that the device can be addressed again. This allows the last byte to be recovered in the event of a communication error. Second and most common, the receiver does not acknowledge the data to deliberately end an operation. For example, during a read operation, the FM24C04A will continue to place data onto the bus as long as the receiver sends acknowledges (and clocks). When a read operation is complete and no more data is needed, the receiver must not acknowledge the last byte. If the receiver acknowledges the last byte, this will cause the FM24C04A to attempt to drive the bus on the next clock while the master is sending a new command such as a Stop command. Slave Address The first byte that the FM24C04A expects after a start condition is the slave address. As shown in Figure 4, the slave address contains the device type, the device select, the page of memory to be accessed, and a bit that specifies if the transaction is a read or a write. Bits 7-4 are the device type and should be set to 1010b for the FM24C04A. The device type allows other types of functions to reside on the 2-wire bus within an identical address range. Bits 3-2 are the device address. If bit 3 matches the A2 pin and bit 2 matches the A1 pin, the device will be selected. Bit 1 is the page select. It specifies the 256-byte block of memory that is targeted for the current operation. Bit 0 is the read/write bit. A 0 indicates a write operation. Word Address After the FM24C04A (as receiver) acknowledges the slave ID, the master will place the word address on the bus for a write operation. The word address is the lower 8-bits of the address to be combined with the 1-bit page select to specify exactly the byte to be written. The complete 9-bit address is latched internally. |
Podobny numer części - FM24C04A_05 |
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Podobny opis - FM24C04A_05 |
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