Document Number: 001-85257 Rev. *M Page 6 of 55
Device Operation
CY14V101QS is a 1-Mbit quad serial interface nvSRAM memory
with a SONOS FLASH nonvolatile element interleaved with an
SRAM element in each memory cell. All the reads and writes to
nvSRAM happen to the SRAM, which gives nvSRAM the unique
capability to handle infinite writes to the memory. The data in
SRAM is secured by a STORE sequence, which transfers the
data to the nonvolatile cells. A small capacitor (VCAP) is used to
AutoStore the SRAM data into the nonvolatile cells when power
goes down providing data integrity. The nonvolatile cells are built
in the reliable SONOS technology make nvSRAM the ideal
choice for data storage.
The 1-Mbit memory array is organized as 128Kbytes. The
memory can be accessed through a standard SPI interface
(Single mode, Dual mode, and Quad mode) up to clock speeds
of 40-MHz with zero-cycle latency for read and write operations.
This SPI interface also supports 108-MHz operations (Single
mode, Dual mode, and Quad mode) with cycle latency for read
operations only. The device operates as a SPI slave and
supports SPI modes 0 and 3 (CPOL, CPHA = [0, 0] and [1, 1]).
All instructions are executed using Chip Select (CS), Serial Input
(SI) (I/O0), Serial Output (SO) (I/O1), and Serial Clock (SCK)
pins in single and dual modes. Quad mode uses WP I/O2 and
I/O3 pins as well for command, address, and data entry.
The device uses SPI opcodes for memory access. The opcodes
support SPI, Dual Data, Dual Addr/Data, Dual I/O, Quad Data,
Quad Addr/Data, and Quad I/O modes for read and write opera-
tions. In addition, four special instructions are included that allow
access to nvSRAM specific functions: STORE, RECALL,
AutoStore Disable (ASDI), and AutoStore Enable (ASEN).
The device has built-in data security features. It provides
hardware and software write-protection through the WP pin and
WRDI instruction respectively. Furthermore, the memory array
block is write-protected through Status register block protect bits.
SRAM Write
All writes to nvSRAM are carried out on the SRAM cells and do
not use any endurance cycles of the SONOS FLASH nonvolatile
memory. This allows you to perform infinite write operations. A
write cycle is initiated through one of the Write instructions:
WRITE, DIW, QIW, DIOW, and QIOW. The Write instructions
consist of a write opcode, three bytes of address, and one byte
of data. Write to nvSRAM is done at SPI bus speed with
zero-cycle latency.
The device allows burst mode writes. This enables write opera-
tions on consecutive addresses without issuing a new Write
instruction. When the last address in memory is reached in burst
mode, the address rolls over to 0x00000 and the device
continues to write.
The SPI write cycle sequence is defined explicitly in the nvSRAM
Read Write Instructions in “SPI Functional Description” on
page 12.
SRAM Read
All reads to nvSRAM are carried out on the SRAM cells at SPI
bus speeds. Read instruction (READ) executes at 40-MHz with
zero cycle latency. It consists of a Read opcode byte followed by
three bytes of address. The data is read out on the data output
pin/pins.
Speeds higher than 40 MHz (up to 108 MHz) require Fast Read
instructions: FAST_READ, DOR, QOR, DIOR, and QIOR. The
Fast Read instructions consist of a Fast Read opcode byte, three
bytes of address, and a dummy/mode byte. The data is read out
on the data output pin/pins.
The device allows burst mode reads. This enables read opera-
tions on consecutive addresses without issuing a new Read
instruction. When the last address in memory is reached in burst
mode, the address rolls over to 0x00000 and the device
continues to read.
The SPI read cycle sequence is defined explicitly in the nvSRAM
Read Write Instructions in “SPI Functional Description” on
page 12.
STORE Operation
STORE operation transfers the data from the SRAM to the
nonvolatile cells. The device stores data using one of the three
STORE operations: AutoStore, activated on device power-down
(requires VCAP); Software STORE, activated by a STORE
instruction; and Hardware STORE, activated by the HSB pin.
During the STORE cycle, the nonvolatile cell is first erased and
then programmed. After a STORE cycle is initiated, read/write to
the device is inhibited until the cycle is completed.
The HSB signal or the WIP bit in Status Register can be
monitored by the system to detect if a STORE cycle is in
progress. The busy status of nvSRAM is indicated by HSB being
pulled LOW or the WIP bit being set to ‘1’. To avoid unnecessary
nonvolatile STOREs, AutoStore and Hardware STORE
operations are ignored unless at least one SRAM write operation
has taken place since the most recent STORE cycle. However,
software initiated STORE cycles are performed regardless of
whether a SRAM write operation has taken place.
AutoStore Operation
The AutoStore operation is a unique feature of nvSRAM, which
automatically stores the SRAM data to the SONOS FLASH
nonvolatile cells during power-down. This STORE makes use of
an external capacitor (VCAP) and enables the device to safely
STORE the data in the nonvolatile memory when power goes
down.
During normal operation, the device draws current from VCC to
charge the capacitor connected to the VCAP pin. When the
voltage on the VCC pin drops below VSWITCH during power-down,
the device inhibits all memory accesses to nvSRAM and
automatically performs a STORE operation using the charge
from the VCAP capacitor. The AutoStore operation is not initiated
if a write cycle has not been performed since last RECALL.