24C01C_07 Datasheet, PDF (6/24 Pages) Microchip Technology – 1K 5.0V I2C ™ Serial EEPROM

24C01C
5.0 DEVICE ADDRESSING
A control byte is the first byte received following the
Start condition from the master device (Figure 5-1).
The control byte consists of a four-bit control code; for
the 24C01C this is set as ‘1010’ binary for read and
write operations. The next three bits of the control byte
are the Chip Select bits (A2, A1, A0). The Chip Select
bits allow the use of up to eight 24C01C devices on the
same bus and are used to select which device is
accessed. The Chip Select bits in the control byte must
correspond to the logic levels on the corresponding A2,
A1 and A0 pins for the device to respond. These bits
are in effect the three Most Significant bits of the word
address.
The last bit of the control byte defines the operation to
be performed. When set to a ‘1’ a read operation is
selected, and when set to a ‘0’ a write operation is
selected. Following the Start condition, the 24C01C
monitors the SDA bus checking the control byte being
transmitted. Upon receiving a ‘1010’ code and appro-
priate Chip Select bits, the slave device outputs an
Acknowledge signal on the SDA line. Depending on the
state of the R/W bit, the 24C01C will select a read or
write operation.
FIGURE 5-1:
CONTROL BYTE FORMAT
Read/Write Bit
Chip Select
Control Code
Bits
S 1 0 1 0 A2 A1 A0 R/W ACK
Start Bit
Slave Address
Acknowledge Bit
5.1 Contiguous Addressing Across
Multiple Devices
The Chip Select bits A2, A1, A0 can be used to expand
the contiguous address space for up to 8K bits by
adding up to eight 24C01C devices on the same bus.
In this case, software can use A0 of the control byte as
address bit A8, A1 as address bit A9, and A2 as
address bit A10. It is not possible to write or read
across device boundaries.
DS21201G-page 6
© 2007 Microchip Technology Inc.