Serial Output (SO)
SO is a push/pull serial data output pin. During a read
cycle, data is shifted out on this pin. Data is clocked
out by the falling edge of the serial clock.
Serial Input (SI)
SI is the serial data input pin. All opcodes, byte
addresses, and data to be written to the memory are
input on this pin. Data is latched by the rising edge of
the serial clock.
Serial Clock (SCK)
The Serial Clock controls the serial bus timing for data
input and output. Opcodes, addresses, or data present
on the SI pin are latched on the rising edge of the
clock input, while data on the SO pin change after the
falling edge of the clock input.
Chip Select (CS)
When CS is high, the X25128 is deselected and the
SO output pin is at high impedance and unless an
internal write operation is underway, the X25128 will
be in the standby power mode. CS low enables the
X25128, placing it in the active power mode. It should
be noted that after power-up, a high to low transition
on CS is required prior to the start of any operation.
Write Protect (WP)
When WP is low and the nonvolatile bit WPEN is “1”,
nonvolatile writes to the X25128 status register are
disabled, but the part otherwise functions normally.
When WP is held high, all functions, including nonvola-
tile writes operate normally. WP going low while CS is
still low will interrupt a write to the X25128 status
register. If the internal write cycle has already been
initiated, WP going low will have no effect on a write.
The WP pin function is blocked when the WPEN bit in
the status register is “0”. This allows the user to install
the X25128 in a system with WP pin grounded and still
be able to write to the status register. The WP pin func-
tions will be enabled when the WPEN bit is set “0”.
HOLD is used in conjunction with the CS pin to select
the device. Once the part is selected and a serial
sequence is underway, HOLD may be used to pause
the serial communication with the controller without
resetting the serial sequence. To pause, HOLD must
be brought low while SCK is Low. To resume commu-
nication, HOLD is brought high, again while SCK is
low. If the pause feature is not used, HOLD should be
held high at all times.
14 Lead SOIC
Not to scale
16 Lead SOIC
8 Lead PDIP
3091 FM 02
Chip Select Input
Serial Clock Input
Write Protect Input
3091 FM T01