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CAT34WC02P-TE13 Datasheet(PDF) 7 Page - Catalyst Semiconductor |
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CAT34WC02P-TE13 Datasheet(HTML) 7 Page - Catalyst Semiconductor |
7 / 10 page CAT34WC02 7 Doc No. 1003, Rev. A memory array is protected and becomes read only. The entire memory becomes write protected regardless of whether the write protect register has been written or not. When WP pin is tied to Vcc, the user cannot program the write protect register. If the WP pin is left floating or tied to Vss, the device can be written into (except the first 128 bytes if the write protect register is programmed). Software The software protection on the CAT34WC02 protects the first 128 bytes of the memory array permanently. Software write protect is implemented by programming the write protect register. A user can write only once to the write protect register and once written it is irrevers- ible (even if you reset the CAT34WC02). The write protection register is written by sending a regular byte write command with the slave address set to 0110 instead of 1010. After the initial acess to the register, the device will not acknowledge any further access to this register. READ OPERATIONS The READ operation for the CAT34WC02 is initiated in the same manner as the write operation with the one exception that the R/ W bit is set to a one. Three different READ operations are possible: Immediate Address READ, Selective READ and Sequential READ. Immediate Address Read The CAT34WC02’s address counter contains the ad- dress of the last byte accessed, incremented by one. In other words, if the last READ or WRITE access was to address N, the READ immediately following would ac- cess data from address N+1. If N = 255 for 34WC02, then the counter will ‘wrap around’ to address 0 and continue to clock out data. After the CAT34WC02 re- ceives its slave address information (with the R/ W bit set to one), it issues an acknowledge, then transmits the 8- bit byte requested. The master device does not send an acknowledge but will generate a STOP condition. Selective Read Selective READ operations allow the Master device to select at random any memory location for a READ operation. The Master device first performs a ‘dummy’ write operation by sending the START condition, slave address and byte address of the location it wishes to read. After the CAT34WC02 acknowledge the word address, the Master device resends the START condi- tion and the slave address, this time with the R/ W bit set to one. The CAT34WC02 then responds with its ac- knowledge and sends the 8-bit byte requested. The master device does not send an acknowledge but will generate a STOP condition. Sequential Read The Sequential READ operation can be initiated by either the Immediate Address READ or Selective READ operations. After the CAT34WC02 sends the initial 8-bit data requested, the Master will respond with an ac- knowledge which tells the device it requires more data. The CAT34WC02 will continue to output a byte for each acknowledge sent by the Master. The operation will terminate operation when the Master fails to respond with an acknowledge, thus sending the STOP condition. The data being transmitted from the CAT34WC02 is outputted sequentially with data from address N fol- lowed by data from address N+1. The READ operation address counter increments all of the CAT34WC02 address bits so that the entire memory array can be read during one operation. If more than the 256 bytes are read out, the counter will “wrap around” and continue to clock out data bytes. 5020 FHD F10 Figure 8. Immediate Address Read Timing SLAVE ADDRESS S A C K DATA N O A C K S T O P P BUS ACTIVITY: MASTER SDA LINE S T A R T SCL SDA 8TH BIT STOP NO ACK DATA OUT 89 K |
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