PSD4235G2 datasheet(25/89 Pages) STMICROELECTRONICS

25 / 89 page

25/89

PSD4235G2

Sector Erase cycle for a period of 100 µs + 20%

unless an additional Sector Erase instruction is de-

coded. After this period, or when the additional

Sector Erase instruction is decoded, the Erase

Time-out Flag (DQ3/DQ11) bit is set to 1.

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).

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 (DQ7/

DQ15) bit is a method of checking whether a Pro-

gram or Erase cycle is in progress or has complet-

ed. 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 (DQ7/DQ15) bit 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 (DQ5/DQ13) bit. When the Data

Polling (DQ7/DQ15) bit matches the correspond-

ing bit of the original data, and the Error Flag

(DQ5/DQ13) bit remains 0, the embedded algo-

rithm is complete. If the Error Flag (DQ5/DQ13) bit

is 1, the MCU should test the Data Polling (DQ7/

DQ15) bit again since the Data Polling (DQ7/

DQ15) bit may have changed simultaneously with

the Error Flag (DQ5/DQ13) bit (see Figure 6).

The Error Flag (DQ5/DQ13) bit is set if either an in-

ternal time-out occurred while the embedded algo-

rithm 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

Data Polling (DQ7/DQ15) bit is 0 until the Erase

cycle is complete. A 1 on the Error Flag (DQ5/

DQ13) bit 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 (DQ7/DQ15) bit and

the Error Flag (DQ5/DQ13) bit.

PSDsoft Express generates ANSI C code func-

tions that implement these Data Polling algo-

rithms.

Figure 6. Data Polling Flowchart

Data Toggle. Checking the Toggle Flag (DQ6/

DQ14) bit is another method of determining wheth-

er a Program or Erase cycle is in progress or has

completed. Figure 7 shows the Data Toggle algo-

rithm.

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 (DQ6/DQ14) bit toggles each time the MCU

READ DQ5 and DQ7

(DQ13 and DQ15)

at Valid Even Address

START

READ DQ7

(DQ15)

Program

or Erase

Cycle failed

Program

or Erase

Cycle is

complete

AI04920

Yes

DQ5

(DQ13)

= 1

DQ7

(DQ15)

Data7

(Data15)

Yes

Issue RESET

instruction

DQ7

(DQ15)

Data7

(Data15)

PSD4235G2 датащи(PDF) 25 Page - STMicroelectronics

PSD4235G2 датащи(HTML) 25 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89

датащи скачать

ссылки URL