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CY14ME256J2-SXIT Datasheet(PDF) 7 Page - Cypress Semiconductor |
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CY14ME256J2-SXIT Datasheet(HTML) 7 Page - Cypress Semiconductor |
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7 / 30 page  CY14MC256J CY14MB256J CY14ME256J Document Number: 001-65233 Rev. *G Page 7 of 30 Slave Device Address Every slave device on an I2C bus has a device select address. The first byte after START condition contains the slave device address with which the master intends to communicate. The seven MSBs are the device address and the LSB (R/W bit) is used for indicating Read or Write operation. The CY14MX256J reserves two sets of upper four MSBs [7:4] in the slave device address field for accessing Memory and Control Registers. The accessing mechanism is described in Memory Slave Device. The nvSRAM product provides two different functionalities: Memory and Control Registers functions (such as serial number and product ID). The two functions of the device are accessed through different slave device addresses. The first four most significant bits [7:4] in the device address register are used to select between the nvSRAM functions. Memory Slave Device The nvSRAM device is selected for Read/Write if the master issues the slave address as 1010b followed by two/three bits of device select. For CY14MX256J1/J3, the device select is three bits and for CY14MX256J2, it is two bits with the third bit don’t care. If the slave address sent by the master matches with the Memory Slave device address then depending on the R/W bit of the slave address, data is either read from (R/W = ‘1’) or written to (R/W = ‘0’) the nvSRAM. The address length for CY14MX256J is 15 bits and thus it requires two address bytes to map the entire memory address location. The dedicated two address bytes represent bit A0 to A14. However, since the address is only 15-bits, it implies that the first MSB bit that is fed in is ignored by the device. Although this bit is ‘don’t care’, Cypress recommends that this bit is treated as 0 to enable seamless transition to higher memory densities. Control Registers Slave Device The Control Registers Slave device includes the Serial Number, Product ID, Memory Control, and Command Register. The nvSRAM Control Register Slave device is selected for Read/Write if the master issues the Slave address as 0011b followed by two/three bits of device select. For CY14MX256J1/J3 device select is three bits and for CY14MX256J2 it is two bits with third bit don’t care. If the slave address sent by the master matches with the Memory Slave device address, then depending on the R/W bit of the slave address, data is either read from (R/W = ‘1’) or written to (R/W = ‘0’) the nvSRAM. Table 1. Slave device Addressing Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 nvSRAM Function Select CY14MX256J Slave Devices 1 0 1 0 Device Select ID R/W Selects Memory Memory, 32 K × 8 0 0 1 1 Device Select ID R/W Selects Control Registers Control Registers - Memory Control Register, 1 × 8 - Serial Number, 8 × 8 - Device ID, 4 × 8 - Command Register, 1 × 8 Figure 8. Memory Slave Device Address handbook, halfpage R/W LSB MSB Slave ID 10 1 0 A2 A0/X A1 Device Select Figure 9. Control Registers Slave Device Address handbook, halfpage R/W LSB MSB Slave ID 0 0 1 1 A2 A0/X A1 Device Select |
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