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PSD4235G2
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reads this location until the embedded algorithm is
complete. The MCU continues to read this loca-
tion, checking the Toggle Flag (DQ6/DQ14) bit
and monitoring the Error Flag (DQ5/DQ13) bit.
When the Toggle Flag (DQ6/DQ14) bit stops tog-
gling (two consecutive reads yield the same val-
ue), and the Error Flag (DQ5/DQ13) bit remains 0,
the embedded algorithm is complete. If the Error
Flag (DQ5/DQ13) bit is 1, the MCU should test the
Toggle Flag (DQ6/DQ14) bit again, since the Tog-
gle Flag (DQ6/DQ14) bit may have changed simul-
taneously with the Error Flag (DQ5/DQ13) bit (see
Figure 7).
Figure 7. Data Toggle Flowchart
The Error Flag (DQ5/DQ13) bit is set if either an in-
ternal time-out occurred while the embedded algo-
rithm attempted to program, or if the MCU
attempted to program a 1 to a bit that was not
erased (not erased is logic 0).
It is suggested (as with all Flash memories) to read
the location again after the embedded program-
ming algorithm has completed, to compare the
word that was written to Flash memory with the
word that was intended to be written.
When using the Data Toggle method after an
Erase cycle, Figure 7 still applies. the Toggle Flag
(DQ6/DQ14) bit toggles until the Erase cycle is
complete. A 1 on the Error Flag (DQ5/DQ13) bit in-
dicates a time-out condition on the Erase cycle, a
0 indicates no error. The MCU can read any even
location within the sector being erased to get the
Toggle Flag (DQ6/DQ14) bit and the Error Flag
(DQ5/DQ13) bit.
PSDsoft Express generates ANSI C code func-
tions which implement these Data Toggling algo-
rithms.
Unlock Bypass.
The Unlock Bypass instruction
allows the system to program words to the Flash
memories faster than using the standard Program
instruction. The Unlock Bypass mode is entered
by first initiating two Unlock cycles. This is followed
by a third Write cycle containing the Unlock By-
pass command, 20h (as shown in Table 29). The
Flash memory then enters the Unlock Bypass
mode.
A two-cycle Unlock Bypass Program instruction is
all that is required to program in this mode. The
first cycle in this instruction contains the Unlock
Bypass Program command, A0h. The second cy-
cle contains the program address and data. Addi-
tional data is programmed in the same manner.
This mode dispense with the initial two Unlock cy-
cles required in the standard Program instruction,
resulting in faster total programming time.
During the unlock bypass mode, only the Unlock
Bypass Program and Unlock Bypass Reset in-
structions are valid.
To exit the Unlock Bypass mode, the system must
issue the two-cycle Unlock Bypass Reset instruc-
tion. The first cycle must contain the data 90h; the
second cycle the data 00h. Addresses are Don’t
Care for both cycles. The Flash memory then re-
turns to Read mode.
Erasing Flash Memory
Flash Bulk Erase.
The Flash Bulk Erase instruc-
tion uses six Write operations followed by a Read
operation of the status register, as described in
Table 29. If any byte of the Bulk Erase instruction
is wrong, the Bulk Erase instruction aborts and the
device is reset to the Read Memory mode.
During a Bulk Erase, the memory status may be
checked by reading the Error Flag (DQ5/DQ13)
bit, the Toggle Flag (DQ6/DQ14) bit, and the Data
Polling (DQ7/DQ15) bit, as detailed in the section
START
READ DQ6
(DQ14)
AI04921
No
No
Yes
Yes
No
Yes
Program
or Erase
Cycle failed
Program
or Erase
Cycle is
complete
Issue RESET
instruction
READ DQ5 and DQ6
(DQ13 and DQ14)
at Valid Even Address
DQ5
(DQ13)
= 1
DQ6
(D=
Toggle
DQ6
(D=
Toggle