UPSD3254 STMICROELECTRONICS [STMicroelectronics], UPSD3254 Datasheet - Page 112

• Manufacturer Part Number: UPSD3254
• Description: Flash Programmable System Devices with 8032 Microcontroller Core
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

UPSD3254A, UPSD3254BV, UPSD3253B, UPSD3253BV
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 53 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 53).
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 53 still applies. the Toggle
Flag Bit (DQ6) toggles until the Erase cycle is
complete. A 1 on the Error Flag Bit (DQ5) indicates
a time-out condition on the Erase cycle; a '0' indi-
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cates 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 53. Data Toggle Flowchart
NO
DQ5 & DQ6
READ DQ6
TOGGLE
TOGGLE
START
READ
FAIL
DQ6
DQ5
DQ6
= 1
=
=
YES
YES
YES
NO
NO
PASS
AI01370B