NAND256-A datasheet(54/57 Pages) STMICROELECTRONICS

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APPENDIX A. HARDWARE INTERFACE EXAMPLES

Nand Flash devices can be connected to a micro-

controller system bus for code and data storage.

For microcontrollers that have an embedded

NAND controller the NAND Flash can be connect-

ed without the addition of glue logic (see

Figure 43.). However a minimum of glue logic is

required for general purpose microcontrollers that

do not have an embedded NAND controller. The

glue logic usually consists of a flip-flop to hold the

Chip Enable, Address Latch Enable and Com-

mand Latch Enable signals stable during com-

mand and address latch operations, and some

logic gates to simplify the firmware or make the de-

sign more robust.

Figure 44. gives an example of how to connect a

NAND Flash to a general purpose microcontroller.

The additional OR gates allow the microcontrol-

ler’s Output Enable and Write Enable signals to be

used for other peripherals. The OR gate between

A3 and CSn maps the flip-flop and NAND I/O in

different address spaces inside the same chip se-

lect unit, which improves the setup and hold times

and simplifies the firmware. The structure uses the

microcontroller DMA (Direct Memory Access) en-

gines to optimize the transfer between the NAND

Flash and the system RAM.

For any interface with glue logic, the extra delay

caused by the gates and flip-flop must be taken

into account. This delay must be added to the mi-

crocontroller’s AC characteristics and register set-

tings to get the NAND Flash setup and hold times.

For mass storage applications (hard disk emula-

tions or systems where a huge amount of storage

is required) NAND Flash memories can be con-

nected together to build storage modules (see Fig-

ure 45.).

Figure 43. Connection to Microcontroller, Without Glue Logic

AI08045b

I/O

CSn

AD(24:16)

Microcontroller

NAND

Flash

PWAITEN

AD17

AD16

VDD

VDD or VSS

or General Purpose I/O

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