PSD934210JIT STMICROELECTRONICS [STMicroelectronics], PSD934210JIT Datasheet - Page 19

• Manufacturer Part Number: PSD934210JIT
• Description: Flash PSD, 3.3V Supply, for 8-bit MCUs 2 Mbit 256 Kbit Dual Flash Memories and 64 Kbit SRAM
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

Programming Flash Memory
Flash memory must be erased prior to being pro-
grammed. A byte of Flash memory is erased to all
1s (FFh), and is programmed by setting selected
bits to 0. The MCU may erase Flash memory all at
once or by-sector, but not byte-by-byte. However,
the MCU may program Flash memory byte-by-
byte.
The primary and secondary Flash memories re-
quire the MCU to send an instruction to program a
byte or to erase sectors (see Table 7).
Once the MCU issues a Flash memory Program or
Erase instruction, it must check for the status bits
for completion. The embedded algorithms that are
invoked 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 (PC3).
Data Polling. Polling on the Data Polling Flag
(DQ7) bit is a method of checking whether a Pro-
gram or Erase cycle is in progress or has complet-
ed. Figure 4 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 byte to be pro-
grammed in Flash memory to check status. The
Data Polling Flag (DQ7) bit of this location be-
comes the complement of b7 of the original data
byte to be programmed. The MCU continues to
poll this location, comparing the Data Polling Flag
(DQ7) bit and monitoring the Error Flag (DQ5) bit.
When the Data Polling Flag (DQ7) bit matches b7
of the original data, and the Error Flag (DQ5) bit
remains 0, the embedded algorithm is complete. If
the Error Flag (DQ5) bit is 1, the MCU should test
the Data Polling Flag (DQ7) bit again since the
Data Polling Flag (DQ7) bit may have changed si-
multaneously with the Error Flag (DQ5) bit (see
Figure 4).
The Error Flag (DQ5) bit 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 the Flash memory with the
byte that was intended to be written.
When using the Data Polling method during an
Erase cycle, Figure 4 still applies. However, the
Data Polling Flag (DQ7) bit is 0 until the Erase cy-
cle is complete. A 1 on the Error Flag (DQ5) bit in-
dicates a time-out condition on the Erase cycle; a
0 indicates no error. The MCU can read any loca-
tion within the sector being erased to get the Data
Polling Flag (DQ7) bit and the Error Flag (DQ5) bit.
PSDsoft Express generates ANSI C code func-
tions which implement these Data Polling algo-
rithms.
Figure 4. Data Polling Flowchart
Data Toggle. Checking the Toggle Flag (DQ6) bit
is a method of determining whether a Program or
Erase cycle is in progress or has completed. Fig-
ure 5 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 of the byte to be pro-
grammed in Flash memory to check status. The
Toggle Flag (DQ6) bit of this location toggles each
time the MCU reads this location until the embed-
ded algorithm is complete. The MCU continues to
read this location, checking the Toggle Flag (DQ6)
bit and monitoring the Error Flag (DQ5) bit. When
the Toggle Flag (DQ6) bit stops toggling (two con-
secutive reads yield the same value), and the Er-
ror Flag (DQ5) bit remains 0, the embedded
algorithm is complete. If the Error Flag (DQ5) bit is
1, the MCU should test the Toggle Flag (DQ6) bit
again, since the Toggle Flag (DQ6) bit may have
changed simultaneously with the Error Flag (DQ5)
bit (see Figure 5).
at VALID ADDRESS
NO
READ DQ5 & DQ7
READ DQ7
START
DATA
DATA
DQ7
DQ5
DQ7
FAIL
= 1
=
=
YES
NO
NO
YES
YES
PSD834F2V
PASS
AI01369B
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