CAT25640
www.onsemi.com
12
Hold Operation
The HOLD input can be used to pause communication
between host and CAT25640. To pause, HOLD
must be
taken low while SCK is low (Figure 11). During the hold
condition the device must remain selected (CS
low). During
the pause, the data output pin (SO) is tri−stated (high
impedance) and SI transitions are ignored. To resume
communication, HOLD
must be taken high while SCK is low.
Design Considerations
The CAT25640 device incorporates Power−On Reset
(POR) circuitry which protects the internal logic against
powering up in the wrong state. The device will power up
into Standby mode after V
CC
exceeds the POR trigger level
and will power down into Reset mode when V
CC
drops
below the POR trigger level. This bi−directional POR
behavior protects the device against ‘brown−out’ failure
following a temporary loss of power.
The CAT25640 device powers up in a write disable state
and in a low power standby mode. A WREN instruction
must be issued prior to any writes to the device.
After power up, the CS
pin must be brought low to enter
a ready state and receive an instruction. After a successful
byte/page write or status register write, the device goes into
a write disable mode. The CS
input must be set high after the
proper number of clock cycles to start the internal write
cycle. Access to the memory array during an internal write
cycle is ignored and programming is continued. Any invalid
op−code will be ignored and the serial output pin (SO) will
remain in the high impedance state.
Figure 11. HOLD Timing
SCK
SO
HIGH IMPEDANCE
Dashed Line = mode (1, 1)
t
LZ
CS
HOLD
t
CD
t
HD
t
HD
t
CD
t
HZ
