After the MCU has been switched to In-System Programming (ISP) Mode, Winbond W78ERD2 MCU Locked Program Recovery can be executed directly, The W78ERD2 equips one 64K byte of main MTP-ROM bank  for  application  program (called  APROM) and one 4K byte of auxiliary MTP-ROM bank for loader program (called LDROM).

In the normal operation, the microcontroller executes the code in the APROM. If  the content of APROM  needs to be modified, the W78ERD2 allows user to activate the In-System  Programming (ISP)  mode  by setting the CHPCON register.

The CHPCON is read-only by default, software must write two specific values 87H, then 59H sequentially to the CHPENR register to enable the CHPCON write attribute. Writing CHPENR register with the values except 87H and 59H will close CHPCON register write attribute.

The W78ERD2 achieves all in-system programming operations including enter/exit ISP Mode, program, erase, read …etc, during device in the idle mode. Setting the bit CHPCON.0 the device will enter in-system programming mode after a wake-up from idle mode from Winbond W78ERD2 MCU Locked Program Recovery.

Because device needs proper time to complete the ISP operations before awaken from idle mode, software may use timer interrupt to control the duration for wake-up from idle mode. This in-system programming feature makes the job easy and efficient in which the application needs to update firmware frequently. In some applications, the  in-system  programming feature make it possible that  the end-user is able to easily update the system firmware by themselves without opening the chassis.

SFRAH,SFRAL:

The objective address of on-chip MTP-ROM in the in-system programming mode.  SFRFAH contains the high-order byte of address, SFRFAL contains the low-order byte of address.

SFRFD:

The programming data for on-chip MTP-ROM in programming mode.

SFRCN:

The control byte of on-chip MTP-ROM programming mode.

SFRCN (C7)

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