Dave Embedded Systems Axel ULite, Hardware Manual

Page: 19 / 65

AXEL ULite Hardware Manual v.1.0.2
3.2.1 Reliable Storage Strategy
Any embedded product requires to be reliable, robust and economic. This
is the reason why DAVE Embedded Systems introduced the usage of a
good combination of memories that works perfectly in their context and
meet all embedded systems goals. NOR and NAND flash are the key
components of this strategy.
[From Wiki]
NOR and NAND flash differ in two important ways:
● the connections of the individual memory cells are different
● the interface provided for reading and writing the memory is
different (NOR allows random-access for reading, NAND allows
only page access)
These two are linked by the design choices made in the development of
NAND flash. A goal of NAND flash development was to reduce the chip
area required to implement a given capacity of flash memory, and
thereby to reduce cost per bit and increase maximum chip capacity so
that flash memory could compete with magnetic storage devices like hard
disks. [...]
Because of the series connection and removal of wordline contacts, a
large grid of NAND flash memory cells will occupy perhaps only 60% of
the area of equivalent NOR cells.
[..] NAND flash's designers realized that the area of a NAND chip, and
thus the cost, could be further reduced by removing the external address
and data bus circuitry. Instead, external devices could communicate with
NAND flash via sequential-accessed command and data registers, which
would internally retrieve and output the necessary data. This design
choice made random-access of NAND flash memory impossible, but the
goal of NAND flash was to replace mechanical hard disks, not to replace
ROMs.
Attribute NAND NOR
Main Application File Storage Code execution
Storage capacity High Low
Cost per bit Better
Active Power Better
Stability Power Better
Write Speed Good
August, 2019 19/65