w49f020 ETC-unknow, w49f020 Datasheet - Page 3

• Manufacturer Part Number: w49f020
• Manufacturer: ETC-unknow

Preliminary W49F020
FUNCTIONAL DESCRIPTION
Read Mode
The read operation of the W49F020 is controlled by CE and OE , both of which have to be low for the
host to obtain data from the outputs. CE is used for device selection. When CE is high, the chip is
de-selected and only standby power will be consumed. OE is the output control and is used to gate data
from the output pins. The data bus is in high impedance state when either CE or OE is high. Refer to the
timing waveforms for further details.
Boot Block Operation
There is an 8K-byte boot block in this device, which can be used to store boot code. The boot block
locates in the first 8K bytes of the memory with the address range from 0000(hex) to 1FFF(hex). For the
specific code, please see Command Codes for Boot Block Lockout Enable.
When the boot block is enabled, data for the designated block cannot be erased or programmed
(programming lockout); other memory locations can be changed by the regular programming method.
When the boot block programming lockout feature is activated, the chip erase function cannot erase the
boot block any longer.
In order to detect whether the boot block feature is set on the 8K-bytes block or not, users can perform
software command sequence to check it. First, enter the product identification mode (see Command
Codes for Identification/Boot Block Lockout Detection for specific code), and then read from address
"0002 hex". If the output data is "1," the boot block programming lockout feature is activated; if the
output data is "0," the lockout feature is inactivated and the block can be erased/programmed.
To return to normal operation, perform a three-byte command sequence (or an alternate single-word
command) to exit the identification mode. For the specific code, see Command Codes for
Identification/Boot Block Lockout Detection.
Chip Erase Operation
The chip-erase mode can be initiated by a six-word command sequence. After the command loading
cycle, the device enters the internal chip erase mode, which is automatically timed and will be completed
in a fast 100 mS (typical). The host system is not required to provide any control or timing during this
operation. If the boot block programming lockout is activated, only the data in the main memory blocks
will be erased to FF(hex), and the data in the boot block will not be erased (remains same as before the
chip erase operation). The entire memory array will be erased to FF hex by the chip erase operation if
the boot block programming lockout feature is not activated. Once the boot block lockout feature is
activated, the chip erase function erase the main memory block but not the boot block. The device will
automatically return to normal read mode after the erase operation completed. Data polling and/or
Toggle Bits can be used to detect end of erase cycle.
Program Operation
The W49F020 is programmed on a byte-by-byte basis. Program operation can only change logical data
"1" to logical data "0." The erase operation (changed entire data in main memory blocks and/or boot
block from "0" to "1") is needed before programming.
The program operation is initiated by a 4-word command cycle (see Command Codes for Byte
Programming). The device will internally enter the program operation immediately after the
byte-program command is entered. The internal program timer will automatically time-out (50 S max. -
Publication Release Date: October 1999
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Revision A1