PSD4235G2V-10U STMICROELECTRONICS [STMicroelectronics], PSD4235G2V-10U Datasheet - Page 32

• Manufacturer Part Number: PSD4235G2V-10U
• Description: Flash In-System Programmable (ISP) Peripherals for 16-bit MCUs
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

PSD4256G6V
Data Toggle
Checking the Toggle Flag Bit (DQ6/DQ14) is an-
other method of determining whether a Program or
Erase cycle is in progress or has completed. Fig-
ure 7 shows the Data Toggle algorithm.
When the MCU issues a Program instruction, the
embedded algorithm within the PSD begins. The
MCU then reads the location to be programmed in
Flash memory to check the status. The Toggle
Flag Bit (DQ6/DQ14) 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/DQ14)
and monitoring the Error Flag Bit (DQ5/DQ13).
When the Toggle Flag Bit (DQ6/DQ14) stops tog-
gling (two consecutive READs yield the same val-
ue), and the Error Flag Bit (DQ5/DQ13) remains
’0,’ the embedded algorithm is complete. If the Er-
ror Flag Bit (DQ5/DQ13) is ’1,’ the MCU should
test the Toggle Flag Bit (DQ6/DQ14) again, since
the Toggle Flag Bit (DQ6/DQ14) may have
changed simultaneously with the Error Flag Bit
(DQ5/DQ13) (see Figure 7).
The Error Flag Bit (DQ5/DQ13) is set if either an
internal time-out occurred while the embedded al-
gorithm attempted to program, 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
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
Bit (DQ6/DQ14) toggles until the Erase cycle is
complete. A ’1’ on the Error Flag Bit (DQ5/DQ13)
indicates 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 Bit (DQ6/DQ14) and the Error
Flag Bit (DQ5/DQ13).
PSDsoft generates ANSI C code functions which
implement these Data Toggling algorithms.
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 Bypass com-
mand, 20h (as shown in Table 29, page 27). 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
32/100
This is preliminary information on a new product now in development or undergoing evaluation. Details are subject to change without notice.
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.
Figure 7. Data Toggle Flowchart
No
at Valid Even Address
READ DQ5 and DQ6
(DQ13 and DQ14)
Issue RESET
READ DQ6
Cycle failed
instruction
Program
or Erase
START
(DQ14)
(DQ13)
(DQ14)
Toggle
(DQ14)
Toggle
DQ6
DQ5
DQ6
= 1
=
=
Yes
Yes
Yes
No
No
complete
Program
or Erase
Cycle is
AI04921