W49L401(T)
Publication Release Date: August 16, 2002
- 3 - Revision A4
6. FUNCTIONAL DESCRIPTION
Read Mode
The read operation of the W49L401(T) 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 to 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.
Reset Operation
The #RESET input pin can be used in some application. When #RESET pin is at high state, the device
is in normal operation mode. When #RESET pin is driven low for at least a period of TRP, it will halt the
device and all outputs are at high impedance state. The device also resets the internal state machine
to read array data. The operation that was interrupted should be reinitiated once the device is ready to
accept another command sequence to assure data integrity. As the high state re-asserted to the
#RESET pin, the device will return to read or standby mode, it depends on the control signals. The
system can read data TRH after the #RESET pin returns to VIH. The other function for #RESET pin is
temporary reset the boot block. By applying the 12V to #RESET pin, the boot block can be
reprogrammed even though the boot block lockout function is enabled.
Boot Block Operation
There is one 8K-word boot block in this device, which can be used to store boot code. It is located in
the first 8K words (for W49L401T, located in the last 8K words) of the memory with the address range
from 0000(hex) to 1FFF(hex). (for W49L401T, address range from 3E000h to 3FFFFh)
See Command Codes for Boot Block Lockout Enable for the specific code. Once this feature is set, the
data for the designated block cannot be erased or programmed (programming lockout); the regular
programming method can change the data in other memory locations.
There is one condition that the lockout feature can be over-ridden. Just apply 12V to #RESET pin, the
lockout feature will temporarily be inactivated and the boot block can be erased/programmed. Once the
#RESET pin returns to CMOS/TTL level, the lockout feature will be activated again.
In order to detect whether the boot block feature is set on the 8K-words block, users can perform
software command sequence: 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 in DQ0 is "1", the boot block programming lockout feature is activated; if the output
data in DQ0 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 200 mS (typical). The host system is not required to provide any control or timing
during this operation. The entire memory array will be erased to FFFF(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 will erase all the blocks/pages except the boot block.