データシートサーチシステム |
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FM24C64 データシート(PDF) 6 Page - Ramtron International Corporation |
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FM24C64 データシート(HTML) 6 Page - Ramtron International Corporation |
6 / 12 page FM24C64 Rev. 3.0 Mar. 2005 6 of 12 S DEVICE ADDRESS 0 By Master By FM24C64 Start Address and Data Stop A ACKNOWLEDGE ADDRESS MSB A DATA BYTE A P ADDRESS LSB A XXX Figure 5. Byte Write S DEVICE ADDRESS 0 By Master By FM24C64 Start Address and Data Stop A ACKNOWLEDGE ADDRESS MSB A DATA BYTE A P ADDRESS LSB A XXX DATA BYTE A Figure 6. Multiple Byte Write Read Operation There are two basic types of read operations. They are current address read and selective address read. In a current address read, the FM24C64 uses the internal address latch to supply the address. In a selective read, the user performs a procedure to set the address to a specific value. Current Address & Sequential Read The FM24C64 uses an internal latch to supply the address for a read operation. A current address read uses the existing value in the address latch as a starting place for the read operation. The system reads from the address immediately following that of the last operation. To perform a current address read, the bus master supplies a device address with the LSB set to 1. This indicates that a read operation is requested. After receiving the complete device address, the FM24C64 will begin shifting out data from the current address on the next clock. The current address is the value held in the internal address latch. Beginning with the current address, the bus master can read any number of bytes. Thus, a sequential read is simply a current address read with multiple byte transfers. After each byte the internal address counter will be incremented. Each time the bus master acknowledges a byte, this indicates that the FM24C64 should read out the next sequential byte. There are four ways to properly terminate a read operation. Failing to properly terminate the read will likely create a bus contention as the FM24C64 attempts to read out additional data onto the bus. The four valid methods are: 1. The bus master issues a no-acknowledge in the 9 th clock cycle and a stop in the 10th clock cycle. This is illustrated in Figures 7-9. This is the preferred method. 2. The bus master issues a no-acknowledge in the 9 th clock cycle and a start in the 10th. 3. The bus master issues a stop in the 9 th clock cycle. 4. The bus master issues a start in the 9 th clock cycle. If the internal address reaches 1FFFh, it will wrap around to 0000h on the next read cycle. Figures 7 and 8 show the proper operation for current address reads. Selective (Random) Read There is a simple technique that allows a user to select a random address location as the starting point for a read operation. This involves using the first three bytes of a write operation to set the internal address followed by subsequent read operations. To perform a selective read, the bus master sends out the device address with the LSB set to 0. This specifies a write operation. According to the write protocol, the bus master then sends the address bytes that are loaded into the internal address latch. After the FM24C64 acknowledges the address, the bus master issues a start condition. This simultaneously aborts the write operation and allows the read command to be issued with the device address LSB set to a 1. The operation is now a current address read. |
同様の部品番号 - FM24C64 |
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同様の説明 - FM24C64 |
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