SI: The serial data input pin accepts op-codes,
addresses and data. In SPI modes (0,0) and (1,1)
input data is latched on the rising edge of the SCK
SO: The serial data output pin is used to transfer data
out of the device. In SPI modes (0,0) and (1,1) data is
shifted out on the falling edge of the SCK clock.
SCK: The serial clock input pin accepts the clock
provided by the host and used for synchronizing
communication between host and CAT25320.
C¯¯S: The chip select input pin is used to
enable/disable the CAT25320. When C¯¯S is high, the
SO output is tri-stated (high impedance) and the
device is in Standby Mode (unless an internal write
operation is in progress). Every communication
session between host and CAT25320 must be
preceded by a high to low transition and concluded
with a low to high transition of the C¯¯S input.
¯W¯P¯: The write protect input pin will allow all write
operations to the device when held high. When ¯W¯P¯
pin is tied low and the WPEN bit in the Status
Register (refer to Status Register description, later in
this Data Sheet) is set to “1”, writing to the Status
Register is disabled.
H¯¯O¯L¯D¯: The H¯¯O¯L¯D¯ input pin is used to pause trans–
mission between host and CAT25320, without
having to retransmit the entire sequence at a later
time. To pause, H¯¯O¯L¯D¯ must be taken low and to
resume it must be taken back high, with the SCK
input low during both transitions. When not used for
pausing, the ¯H¯O¯L¯D¯ input should be tied to VCC,
either directly or through a resistor.
The CAT25320 device supports the Serial Peripheral
Interface (SPI) bus protocol, modes (0,0) and (1,1). The
device contains an 8-bit instruction register. The
instruction set and associated op-codes are listed in
Reading data stored in the CAT25320 is accomplished
by simply providing the READ command and an
address. Writing to the CAT25320, in addition to a
WRITE command, address and data, also requires
enabling the device for writing by first setting certain bits
in a Status Register, as will be explained later.
After a high to low transition on the C¯¯S input pin, the
CAT25320 will accept any one of the six instruction op-
codes listed in Table 1 and will ignore all other possible
8-bit combinations. The communication protocol follows
the timing from Figure 1.
Table 1: Instruction Set
Enable Write Operations
Disable Write Operations
Read Status Register
Write Status Register
Read Data from Memory
Write Data to Memory
Figure 1. Synchronous Data Timing
Note: Dashed Line = mode (1, 1) - - - - - -
Doc. No. 1111 Rev. E
4 © 2007 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice