24LC21A

DS21160F-page 14

 2003 Microchip Technology Inc.

8.0

PIN DESCRIPTIONS

8.1

SDA

This pin is used to transfer addresses and data into and

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

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

Ω for 100 kHz, 2 KΩ for 400 kHz).

For normal data transfer in the Bidirectional mode, SDA

is allowed to change only during SCL low. Changes

during SCL high are reserved for indicating the Start

and Stop conditions.

8.2

SCL

This pin is the clock input for the Bidirectional 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

Bidirectional mode. It must remain high for the chip to

continue operation in the Transmit-only mode.

8.3

VCLK

This pin is the clock input for the Transmit-only mode

(DDC1). In the Transmit-only mode, each bit is clocked

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

mode, a high logic level is required on this pin to enable

write capability.