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M34D64-W

64 Kbit Serial I²C Bus EEPROM With Hardware Write Control on Top Quarter of Memory

STMicroelectronics 

M34D64

SIGNAL DESCRIPTION

Serial Clock (SCL)

This input signal is used to strobe all data in and

out of the device. In applications where this signal

is used by slave devices to synchronize the bus to

a slower clock, the bus master must have an open

drain output, and a pull-up resistor must be con-

nected from Serial Clock (SCL) to VCC. (Figure 5

indicates how the value of the pull-up resistor can

be calculated). In most applications, though, this

method of synchronization is not employed, and

so the pull-up resistor is not necessary, provided

that the bus master has a push-pull (rather than

open drain) output.

Serial Data (SDA)

This bi-directional signal is used to transfer data in

or out of the device. It is an open drain output that

may be wire-OR’ed with other open drain or open

collector signals on the bus. A pull up resistor must

be connected from Serial Data (SDA) to VCC. (Fig-

ure 5 indicates how the value of the pull-up resistor

can be calculated).

Chip Enable (E0, E1, E2)

These input signals are used to set the value that

is to be looked for on the three least significant bits

(b3, b2, b1) of the 7-bit Device Select Code. These

inputs must be tied to VCC or VSS, to establish the

Device Select Code.

Write Control (WC)

The hardware Write Control pin (WC) is useful for

protecting the top quarter of the memory (as

shown in Figure 4) from inadvertent erase or write.

The Write Control signal is used to enable

(WC=VIL) or disable (WC=VIH) write instructions to

the top quarter of the memory area. When uncon-

nected, the WC input is internally read as VIL, and

write operations are allowed.

Figure 4. Memory Map showing Write Control

Area

1FFFh

Write Controlled

Area

1800h

1000h

0800h

0000h

AI03114C

Figure 5. Maximum RL Value versus Bus Capacitance (CBUS) for an I2C Bus

VCC

20

16

12

8

4

0

10

fc = 100kHz

fc = 400kHz

100

CBUS (pF)

RL

SDA

MASTER

SCL

RL

CBUS

1000

CBUS

AI01665

3/21

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