23A640_10 Datasheet, PDF (13/28 Pages) Microchip Technology – 64K SPI Bus Low-Power Serial SRAM

3.0 PIN DESCRIPTIONS
The descriptions of the pins are listed in Table 3-1.
TABLE 3-1: PIN FUNCTION TABLE
Name
CS
SO
VSS
SI
SCK
HOLD
VCC
PDIP/SOIC
TSSOP
1
2
4
5
6
7
8
Function
Chip Select Input
Serial Data Output
Ground
Serial Data Input
Serial Clock Input
Hold Input
Supply Voltage
3.1 Chip Select (CS)
A low level on this pin selects the device. A high level
deselects the device and forces it into Standby mode.
When the device is deselected, SO goes to the high-
impedance state, allowing multiple parts to share the
same SPI bus. After power-up, a low level on CS is
required, prior to any sequence being initiated.
3.2 Serial Output (SO)
The SO pin is used to transfer data out of the 23X640.
During a read cycle, data is shifted out on this pin after
the falling edge of the serial clock.
3.3 Serial Input (SI)
The SI pin is used to transfer data into the device. It
receives instructions, addresses and data. Data is
latched on the rising edge of the serial clock.
3.4 Serial Clock (SCK)
The SCK is used to synchronize the communication
between a master and the 23X640. Instructions,
addresses or data present on the SI pin are latched on
the rising edge of the clock input, while data on the SO
pin is updated after the falling edge of the clock input.
23X640
3.5 Hold (HOLD)
The HOLD pin is used to suspend transmission to the
23X640 while in the middle of a serial sequence without
having to retransmit the entire sequence again. It must
be held high any time this function is not being used.
Once the device is selected and a serial sequence is
underway, the HOLD pin may be pulled low to pause
further serial communication without resetting the
serial sequence. The HOLD pin must be brought low
while SCK is low, otherwise the HOLD function will not
be invoked until the next SCK high-to-low transition.
The 23X640 must remain selected during this
sequence. The SI, SCK and SO pins are in a high-
impedance state during the time the device is paused
and transitions on these pins will be ignored. To resume
serial communication, HOLD must be brought high
while the SCK pin is low, otherwise serial
communication will not resume. Lowering the HOLD
line at any time will tri-state the SO line.
Hold functionality is disabled by the STATUS register
bit.
 2010 Microchip Technology Inc.
DS22126D-page 13