AM24LC21 datasheet(11/13 Pages) ETC

11 / 13 page

AM24LC21

Dual Mode, 1K-bits (128 x 8) 2-Wire Serial EEPROM

(Preliminary)

Anachip Corp.

www.anachip.com.tw

Rev 0.0 Aug 10, 2002

11/13

Control

Byte

Word

address

Control

Byte

Bus activity

SDA Line

Bus activity

Master

Data(n)

Figure 7-2. Random read

Data(n)

Data(n+1)

Data(n+2)

Bus activity

SDA Line

Bus activity

Master

Data(n+X)

Contro

Byte

Figure 7-3. Sequential read

Pin Descriptions (Continued)

SDA

This pin is used to transfer addresses and data into

and out of the device, when the device is in the

bi-directional mode. In the transmit-only mode,

which only allows data to be read from the device,

data is also transferred on the SDA pin. This pin is

an open drain terminal, therefore the SDA bus

requires a pull-up resistor to VCC (typical 10k for

100 Khz, 1k for 400 Khz).

For normal data transfer in the bi-directional mode,

SDA is allowed to change only during SCL low.

Changes during SCL high are reserved for

indicating the START and STOP conditions.

SCL

This pin is the clock input for the bi-directional

mode, and is used to synchronize data transfer to

and from the device. It is also used as the signaling

input to switch the device from the transmit only

mode to the bi-directional mode. It must remain

high for the chip to continue operation in the

transmit only mode.

VCLK

This pin is the clock input for the transmit only

mode. In the transmit only mode, each bit is

clocked out on the rising edge of this signal. In the

bi-directional mode, a high logic level is required on

this pin to enable write capability.

When using the AM24LC21 in the bi-directional

Mode, the VCLK pin operates as the write protect

control pin. Setting VCLK high allows normal write

operations, while setting VCLK low prevents writing

to any location in the array. Connecting the VCLK

pin to VSS would allow the AM24LC21 to operate

as a serial ROM, although this configuration would

prevent using the device in the transmit-only mode.

If WP is connected to GND, PROGRAM operation

onto the whole memory will not be executed. READ

operation are possible. If WP is connected to Vcc,

normal

memory

operation

enabled,

READ/ WRITE over the entire memory is possible.

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