W19B(L)320ST/B
•
A read cycle to an address containing a sector address (SA), and the address 02h on A7-A0 in
word mode (or the address 04h on A6-A-1 in byte mode) returns 01h if the sector is protected, or
00h if it is unprotected.
To return to read mode (or erase-suspend-read mode if the device was previously in Erase Suspend),
the system must write the reset command.
6.2.4
Enter Security Sector/Exit Security Sector Command Sequence
The Security Sector region provides a secured data area containing a random, sixteen-byte electronic
serial number (ESN). The system can access the Security Sector region by issuing the three-cycle
Enter Security Sector command sequence. The device continues to access the Security Sector region
until the system issues the four-cycle Exit Security Sector command sequence. The Exit Security
Sector command sequence returns the device to normal operation. See “Security Sector Flash
Memory Region” for further information.
6.2.5
Byte/Word Program Command Sequence
The device can be programmed either by word or byte, which depending on the state of the #BYTE
pin. Programming is a four-bus-cycle operation. The program command sequence is initiated by
writing two unlock write cycles, followed by the program setup command. The program address and
data are written next, which in turn initiate the Embedded Program algorithm. The device automatically
provides internally generated program pulses and verifies the programmed cell margin.
Once the Embedded Program algorithm is complete, the device then returns to the read mode and
addresses are no longer latched. The system can determine the status of the program operation by
using DQ7, DQ6, or RY/#BY. Please refer to the Write Operation Status section for bits' information.
Any commands written to the device during the Embedded Program Algorithm are ignored. Please
note that a hardware reset will immediately stop the program operation. The program command
sequence should be reinitiated when the device has returned to the read mode, in order to ensure
data integrity.
Programming is allowed in any sequence and across sector boundaries. A bit cannot be programmed
from “0” back to “1.” If trying to do so may cause that device to set DQ5 = 1, or cause the DQ7 and
DQ6 status bits to indicate that the operation is successful. However, a succeeding read will show that
the data is still “0.” Only erase operations can change “0” to “1.”
6.2.6
Unlock Bypass Command Sequence
The unlock bypass feature provides the system to program bytes or words to device which is faster
than using the standard program command sequence. The unlock bypass command sequence is
initiated by first writing two unlock cycles. And a third write cycle containing the unlock bypass
command, 20h, is followed. Then, the device enters into the unlock bypass mode. A two-cycle unlock
bypass program command sequence is all that required to program in this mode. The first cycle in this
sequence contains the unlock bypass program command, A0h; the second cycle contains the
program address and data. In the same manner, additional data is programmed. This mode dispenses
with the initial two unlock cycles which required in the standard program command sequence,
resulting in faster total programming time.
All through the unlock bypass mode, only the Unlock Bypass Program and Unlock Bypass Reset
commands are valid. The system must issue the two-cycle unlock bypass reset command sequence
to exit the unlock bypass mode. The first cycle must contain the data 90h. The second cycle need to
contain the data 00h. Then, the device returns to the read mode.
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