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DS28CZ04: 4Kb I2C/SMBus EEPROM with Nonvolatile PIO
Read and Write
From the master’s point of view, the DS28CZ04 behaves like an memory device with an address range of 512
bytes. As indicated in the Memory Map, Figure 2, the DS28CZ04 has different types of memory: SRAM, EEPROM
and read-only areas. The write behavior depends on the memory type and the characteristics of the location that is
addressed. The SRAM registers can be written from 1 byte to multiple bytes at a time. The EEPROM can be
written from 1 byte to 16 or 8 bytes at a time, depending on the memory location.
To write to the DS28CZ04, the master must address the device in write access mode, i.e., the slave address must
be sent with the direction bit set to 0. The slave address also determines which of the memory halves is accessed.
The next byte sent in write access mode is the address of the memory location to be written to (“write pointer”) or to
start reading from (“read pointer”) if the write access is terminated without sending data (“dummy write”). Additional
bytes are taken as data for the addressed memory location.
To read from the DS28CZ04, the master must address the device in read access mode, i.e., the slave address
must be sent with the direction bit set to 1. The read pointer determines the location from which the master starts
reading. To set the pointer, the DS28CZ04 must be addressed in write access mode, as described above.
Write Access
Due to the different memory types, special function registers, PIO access registers and address modes, there are
several cases to be distinguished:
? Normal EEPROM
? Short EEPROM
? Special EEPROM
? Reserved
? SRAM Write
? PIO direct
EEPROM block of 16 bytes
EEPROM block of 8 bytes
EEPROM block of 16 bytes with one or more non-writeable bytes
Block of 16 non-writeable bytes
SRAM bytes including PIO Read/Write Access Registers
PIO Read/Write Access Registers only
Table 1A maps the various cases to the applicable memory addresses and explains the device behavior in detail.
All EEPROM writes depend on the state of WP pin. Only when the EEPROM is not write-protected (WP pin state =
0) is data accepted and transferred to the EEPROM. When writing to PIO Read/Write Registers, either by running
into their address range or by addressing them directly, one needs to further distinguish between PIO Multi-
Address Mode and PIO Single Address Mode. The address mode is selected through the ADMD bit of the Direction
and Control/Status Register (Device Address A0h) at address 7Ah. In Multi-Address Mode, each PIO occupies one
memory address whereas in Single-Address Mode all PIOs share a single address. See the PIO Read/Write
Access Registers description for details. The PIO address mode does not affect the device behavior when writing
to the EEPROM sections.
Writing to EEPROM Locations
If the DS28CZ04 is addressed in write access mode, any data bytes that follow the address are written to a 16-byte
buffer, beginning at an offset that is determined by the 4 least significant bits of the target address. This buffer is
initialized (pre-loaded) with data from the addressed 16-byte EEPROM block. Incoming data replaces pre-loaded
data. With every byte received, the buffer's write pointer as well as the read pointer is incremented. If the buffer's
write pointer has reached its maximum value of 1111b (normal EEPROM and special EEPROM) or 0111b (short
EEPROM) and additional data is received, the pointer wraps around (rolls over) and the incoming data is written to
the beginning of the EEPROM write buffer and continuing. The same wrap-around applies to the 4 least-significant
bits of the read pointer. This way the read pointer maintains the last address accessed during a write operation,
incremented by one. The transfer from the buffer to the EEPROM begins when the master generates a STOP
condition. Until the write cycle is completed, the DS28CZ04 is busy for the duration of t PROG .
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