1994-2012 Microchip Technology Inc. DS21095K-page 13
24LC21
8.0 PIN DESCRIPTIONS
TABLE 8-1: PIN FUNCTION TABLE
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
V
CC (typical 10K for 100 kHz, 2K 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.
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.
Name Function
V
SS Ground
SDA Serial Address/Data I/O
SCL Serial Clock (Bidirectional mode)
V
CLK Serial Clock (Transmit-only mode)
V
CC +2.5V to 5.5V Power Supply
NC No Connection
21095K.book Page 13 Wednesday, December 5, 2012 2:28 PM
