Datasheet
24C01C
DS21201K-page 8 1997-2012 Microchip Technology Inc.
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.
For the SOT-23 package, the A2 address pin is not
available. During device addressing, the A2 Chip
Select bit should be set to ‘0’.
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
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 sequentially read
across device boundaries.
For the SOT-23 package, up to four 24C01C devices
can be added for up to 4K bits of address space. In this
case, software can use A0 of the control byte
as
address bit A8, and A1 as address bit A9. It is not pos-
sible to sequentially read across device boundaries.
1010A2 A1 A0SACKR/W
Control Code
Chip Select
Bits
Slave Address
Acknowledge Bit
Start Bit
Read/Write
Bit