24LC025T-/ST データシートの表示（PDF） - Microchip Technology
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24LC025T-/ST Datasheet PDF : 12 Pages
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24LC024/24LC025
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
24LC024/24LC025 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 24LC024/
24LC025 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 signifi-
cant bits of the word address.
The last bit of the control byte defines the operation to
be performed. When set to a one a read operation is
selected, and when set to a zero a write operation is
selected. Following the start condition, the 24LC024/
24LC025 monitors the SDA bus checking the control
byte being transmitted. Upon receiving a 1010 code
and appropriate chip select bits, the slave device out-
puts an acknowledge signal on the SDA line. Depend-
ing on the state of the R/W bit, the 24LC024/24LC025
will select a read or write operation.
FIGURE 5-1: CONTROL BYTE FORMAT
Read/Write Bit
Control Code
Chip Select
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 16K bits by add-
ing up to eight 24LC024/24LC025 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.
DS21210A-page 6
Preliminary
© 1997 Microchip Technology Inc.
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