PSD4235G2V-10U STMICROELECTRONICS [STMicroelectronics], PSD4235G2V-10U Datasheet - Page 31

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

PROGRAMMING FLASH MEMORY
Flash memory must be erased prior to being pro-
grammed. The MCU may erase Flash memory all
at once or by-sector. Although erasing Flash mem-
ory occurs on a sector or device basis, program-
ming Flash memory occurs on a word basis.
The primary and secondary Flash memories re-
quire the MCU to send an instruction to program a
word or to erase sectors (see Table 29, page 27).
Once the MCU issues a Flash memory Program or
Erase instruction, it must check the status bits for
completion. The embedded algorithms that are in-
voked inside the PSD support several means to
provide status to the MCU. Status may be checked
using any of three methods: Data Polling, Data
Toggle, or Ready/Busy (PE4) signal.
Data Polling
Polling on the Data Polling Bit (DQ7/DQ15) is a
method of checking whether a Program or Erase
cycle is in progress or has completed. Figure 6
shows the Data Polling algorithm.
When the MCU issues a Program instruction, the
embedded algorithm within the PSD begins. The
MCU then reads the location of the word to be pro-
grammed in Flash memory to check the status.
The Data Polling Bit (DQ7/DQ15) becomes the
complement of the corresponding bit of the original
data word to be programmed. The MCU continues
to poll this location, comparing data and monitor-
ing the Error Flag Bit (DQ5/DQ13). When the Data
Polling Bit (DQ7/DQ15) matches the correspond-
ing bit of the original data, and the Error Flag Bit
(DQ5/DQ13) remains ’0,’ the embedded algorithm
is complete. If the Error Flag Bit (DQ5/DQ13) is ’1,’
the MCU should test the Data Polling Bit (DQ7/
DQ15) again since the Data Polling Bit (DQ7/
DQ15) may have changed simultaneously with the
Error Flag Bit (DQ5/DQ13) (see Figure 6).
The Error Flag Bit (DQ5/DQ13) is set if either an
internal time-out occurred while the embedded al-
gorithm attempted to program the location 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 the Flash memory with the
word that was intended to be written.
When using the Data Polling method during an
Erase cycle, Figure 6 still applies. However, the
This is preliminary information on a new product now in development or undergoing evaluation. Details are subject to change without notice.
Data Polling Bit (DQ7/DQ15) is ’0’ 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 Data Polling Bit (DQ7/DQ15) and the Error
Flag Bit (DQ5/DQ13).
PSDsoft generates ANSI C code functions that im-
plement these Data Polling algorithms.
Figure 6. Data Polling Flowchart
No
at Valid Even Address
READ DQ5 and DQ7
(DQ13 and DQ15)
Issue RESET
READ DQ7
Cycle failed
instruction
(Data15)
(Data15)
Program
or Erase
START
(DQ15)
(DQ13)
(DQ15)
(DQ15)
Data7
Data7
DQ7
DQ5
DQ7
= 1
=
=
No
Yes
No
Yes
Yes
PSD4256G6V
complete
Program
or Erase
Cycle is
AI04920
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