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There are three basic typesof read operations

 

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 Read operations are initiated in the same way as writeoperations with the exception that the R/W bit of thecontrol byte is set to one. There are three basic typesof read operations: current address read, random read,and sequential read.6.1 Current Address ReadThe 24XX64 contains an address counter that main-tains the address of the last word accessed, internallyincremented by one.

  Therefore, if the previous readaccess was to address n (n is any legal address), thenext current address read operation would access datafrom address n + 1. Upon receipt of the control byte with R/W bit set to one,the 24XX64 issues an acknowledge and transmits theeight bit data word. The master will not acknowledgethe transfer but does generate a STOP condition andthe 24XX64 discontinues transmission.6.2 Random ReadRandom read operations allow the master to accessany memory location in a random manner. To performthis type of read operation, first the word address mustbe set.

  This is done by sending the word address to the24XX64 as part of a write operation (R/W bit set to 0).After the word address is sent, the master generates aSTART condition following the acknowledge. This ter-minates the write operation, but not before the internaladdress pointer is set.

  Then the master issues thecontrol byte again but with the R/W bit set to a one. The24XX64 will then issue an acknowledge and transmitthe 8-bit data word. The master will not acknowledgethe transfer but does generate a STOP condition whichcauses the 24XX64 to discontinue transmission.

  After a random read command, the inter-nal address counter will point to the address locationfollowing the one that was just read. 6.3 Sequential ReadSequential reads are initiated in the same way as a ran-dom read except that after the 24XX64 transmits thefirst data byte, the master issues an acknowledge asopposed to the STOP condition used in a random read.This acknowledge directs the 24XX64 to transmit thenext sequentially addressed 8-bit word.

  Following the final byte transmitted to the master, themaster will NOT generate an acknowledge but will gen-erate a STOP condition. To provide sequential readsthe 24XX64 contains an internal address pointer whichis incremented by one at the completion of each oper-ation. This address pointer allows the entire memorycontents to be serially read during one operation. Theinternal address pointer will automatically roll over fromaddress 1FFF to address 0000 if the master acknowl-edges the byte received from the array address 1FFF.


by pendencea | 2019-11-12 18:02 | 科技

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