ST & T UPSD3212C - Manual (Page 99)

99/163
uPSD3212A, uPSD3212C, uPSD3212CV
Data Toggle. Checking the Toggle Flag Bit
(DQ6) is a method of determining whether a Pro-
gram or Erase cycle is in progress or has complet-
ed. Figure
49 shows the Data Toggle algorithm.
When the MCU issues a Program instruction, the
embedded algorithm begins. The MCU then reads
the location of the byte to be programmed in Flash
memory to check status. The Toggle Flag Bit
(DQ6) of this location toggles each time the MCU
reads this location until the embedded algorithm is
complete. The MCU continues to read this loca-
tion, checking the Toggle Flag Bit (DQ6) and mon-
itoring the Error Flag Bit (DQ5). When the Toggle
Flag Bit (DQ6) stops toggling (two consecutive
reads yield the same value), and the Error Flag Bit
(DQ5) remains '0,' the embedded algorithm is
complete. If the Error Flag Bit (DQ5) is '1,' the
MCU should test the Toggle Flag Bit (DQ6) again,
since the Toggle Flag Bit (DQ6) may have
changed simultaneously with the Error Flag Bit
(DQ5) (see Figure
49 ).
The Error Flag Bit(DQ5) is set if either an internal
time-out occurred while the embedded algorithm
attempted to program the byte, or if the MCU at-
tempted 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
byte that was written to Flash memory with the
byte that was intended to be written.
When using the Data Toggle method after an
Erase cycle, Figure
49 still applies. the Toggle
Flag Bit (DQ6) toggles until the Erase cycle is
complete. A '1' on the Error Flag Bit (DQ5) indi-
cates a time-out condition on the Erase cycle; a '0'
indicates no error. The MCU can read any location
within the sector being erased to get the Toggle
Flag Bit (DQ6) and the Error Flag Bit (DQ5).
PSDsoft Express generates ANSI C code func-
tions which implement these Data Toggling algo-
rithms.
Figure 49. Data Toggle Flowchart
READ
DQ5 & DQ6
START
READ DQ6
FAIL PASS
AI01370B
DQ6
=
TOGGLE
NO
NO
YES
YES
DQ5
= 1
NO
YES
DQ6
=
TOGGLE