PSD4235G2-12UT datasheet(36/124 Pages) STMICROELECTRONICS

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PSD4235G2V

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7.2

Reading Flash memory

Under typical conditions, the MCU may read the primary Flash memory, or secondary Flash

memory, using READ operations just as it would a ROM or RAM device. Alternately, the

MCU may use READ operations to obtain status information about a Program or Erase

cycle that is currently in progress. Lastly, the MCU may use instructions to read special data

from these memory blocks. The following sections describe these READ functions.

7.3

Read memory contents

Primary Flash memory and secondary Flash memory are placed in the READ mode after

Power-up, chip reset, or a Reset Flash instruction (see Table 28). The MCU can read the

memory contents of the primary Flash memory, or the secondary Flash memory by using

READ operations any time the READ operation is not part of an instruction.

7.4

Read Primary Flash identifier

The primary Flash memory identifier is read with an instruction composed of 4 operations: 3

specific WRITE operations and a READ operation (see Table 28). The identifier for the

primary Flash memory is E8h. The secondary Flash memory does not support this

instruction.

7.5

Read Memory Sector Protection status

The Flash memory Sector Protection Status is read with an instruction composed of four

operations: three specific WRITE operations and a READ operation (see Table 28). The

READ operation produces 01h if the Flash memory sector is protected, or 00h if the sector

is not protected.

The sector protection status for all NVM blocks (primary Flash memory, or secondary Flash

memory) can be read by the MCU accessing the Flash Protection and Flash Boot Protection

registers in PSD I/O space. See Section 10.1: Flash Memory Sector Protect, for register

definitions.

7.6

Reading the Erase/Program status bits

The PSD provides several status bits to be used by the MCU to confirm the completion of an

Erase or Program cycle of Flash memory. These status bits minimize the time that the MCU

spends performing these tasks and are defined in Table 29. The status byte resides in an

even location, and can be read as many times as needed. Also note that DQ15-DQ8 is an

even byte for Motorola MCUs with a 16-bit data bus.

For Flash memory, the MCU can perform a READ operation to obtain these status bits while

an Erase or Program instruction is being executed by the embedded algorithm. See

Section 8: Programming Flash memory, for details.

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