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24C01C-IST Datasheet(PDF) 9 Page - Microchip Technology |
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24C01C-IST Datasheet(HTML) 9 Page - Microchip Technology |
9 / 12 page 24C01C © 1997 Microchip Technology Inc. Preliminary DS21201A-page 9 8.0 READ OPERATIONS Read operations are initiated in the same way as write operations with the exception that the R/W bit of the slave address is set to one. There are three basic types of read operations: current address read, random read, and sequential read. 8.1 Current Address Read The 24C01C contains an address counter that main- tains the address of the last word accessed, internally incremented by one. Therefore, if the previous read access was to address n, the next current address read operation would access data from address n + 1. Upon receipt of the slave address with the R/W bit set to one, the 24C01C issues an acknowledge and transmits the eight bit data word. The master will not acknowledge the transfer but does generate a stop condition and the 24C01C discontinues transmission (Figure 8-1). 8.2 Random Read Random read operations allow the master to access any memory location in a random manner. To perform this type of read operation, first the word address must be set. This is done by sending the word address to the 24C01C as part of a write operation. After the word address is sent, the master generates a start condition following the acknowledge. This terminates the write operation, but not before the internal address pointer is set. Then the master issues the control byte again but with the R/W bit set to a one. The 24C01C will then issue an acknowledge and transmits the eight bit data word. The master will not acknowledge the transfer but does generate a stop condition and the 24C01C dis- continues transmission (Figure 8-2). After this com- mand, the internal address counter will point to the address location following the one that was just read. 8.3 Sequential Read Sequential reads are initiated in the same way as a ran- dom read except that after the 24C01C transmits the first data byte, the master issues an acknowledge as opposed to a stop condition in a random read. This directs the 24C01C to transmit the next sequentially addressed 8-bit word (Figure 8-3). To provide sequential reads the 24C01C contains an internal address pointer which is incremented by one at the completion of each operation. This address pointer allows the entire memory contents to be serially read during one operation. The internal address pointer will automatically roll over from address 7F to address 00. FIGURE 8-1: CURRENT ADDRESS READ FIGURE 8-2: RANDOM READ FIGURE 8-3: SEQUENTIAL READ BUS ACTIVITY MASTER SDA LINE BUS ACTIVITY P S S T O P CONTROL BYTE S T A R T DATA A C K N O A C K S P S BUS ACTIVITY MASTER SDA LINE BUS ACTIVITY S T A R T S T O P CONTROL BYTE A C K WORD ADDRESS (n) CONTROL BYTE S T A R T DATA (n) A C K A C K N O A C K BUS ACTIVITY MASTER SDA LINE BUS ACTIVITY CONTROL BYTE DATA n DATA n + 1 DATA n + 2 DATA n + X N O A C K A C K A C K A C K A C K S T O P P |
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