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X4285S8I-2.7 Datasheet(PDF) 11 Page - Xicor Inc. |
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X4285S8I-2.7 Datasheet(HTML) 11 Page - Xicor Inc. |
11 / 22 page X4283/85 – Preliminary Information Characteristics subject to change without notice. 11 of 22 REV 1.17 11/27/00 www.xicor.com Serial Read Operations Read operations are initiated in the same manner as write operations with the exception that the R/W bit of the Slave Address Byte is set to one. There are three basic read operations: Current Address Reads, Ran- dom Reads, and Sequential Reads. Current Address Read Internally the device contains an address counter that maintains the address of the last word read incre- mented by one. Therefore, if the last read was to address n, the next read operation would access data from address n+1. On power up, the address of the address counter is undefined, requiring a read or write operation for initialization. Upon receipt of the Slave Address Byte with the R/W bit set to one, the device issues an acknowledge and then transmits the eight bits of the Data Byte. The mas- ter terminates the read operation when it does not respond with an acknowledge during the ninth clock and then issues a stop condition. Refer to Figure 12 for the address, acknowledge, and data transfer sequence. It should be noted that the ninth clock cycle of the read operation is not a “don’t care.” To terminate a read operation, the master must either issue a stop condi- tion during the ninth cycle or hold SDA HIGH during the ninth clock cycle and then issue a stop condition. Figure 12. Current Address Read Sequence S t a r t S t o p Slave Address Data A C K SDA Bus Signals from the Slave Signals from the Master 1 1 0 1 0 Random Read Random read operation allows the master to access any memory location in the array. Prior to issuing the Slave Address Byte with the R/W bit set to one, the master must first perform a “dummy” write operation. The master issues the start condition and the Slave Address Byte, receives an acknowledge, then issues the Word Address Bytes. After acknowledging receipts of the Word Address Bytes, the master immediately issues another start condition and the Slave Address Byte with the R/W bit set to one. This is followed by an acknowledge from the device and then by the eight bit word. The master terminates the read operation by not responding with an acknowledge and then issuing a stop condition. Refer to Figure 13 for the address, acknowledge, and data transfer sequence. Figure 13. Random Address Read Sequence 0 Slave Address Word Address Byte 1 A C K A C K S t a r t S t o p Slave Address Data A C K 1 S t a r t SDA Bus Signals from the Slave Signals from the Master Word Address Byte 0 A C K 0 1 0 1 |
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