The Microchip Technology Inc. 24LCS22A is a 256 x 8-bit
dual-mode Electrically Erasable PROM (EEPROM). This
device is designed for use in applications requiring
storage and serial transmission of configuration and
control information. Two modes of operation have been
implemented: Transmit-Only mode (1 Kbit) and
Bidirectional mode (2 Kbit). Upon power-up, the device
will be in the Transmit-Only mode, sending a serial bit
stream of the memory array from 00h to 7Fh, clocked by
the VCLK pin. A valid high-to-low transition on the SCL pin
will cause the device to enter the Transition mode, and
look for a valid control byte on the I2C bus. If it detects a
valid control byte from the master, it will switch into
Bidirectional mode, with byte selectable read/write
capability of the entire 2K memory array using SCL. If no
control byte is received, the device will revert to the Transmit-
Only mode after it receives 128 consecutive VCLK
pulses while the SCL pin is idle. The 24LCS22A is available
in standard 8-pin PDIP and SOIC packages. The
24LCS22A features a flexible Write-Protect pin which is
enabled by writing to address 7Fh (usually the checksum
in VESA? applications.