C8051F70X_0910 Datasheet, PDF (135/290 Pages) Silicon Laboratories – Mixed Signal ISP Flash MCU Family

C8051F70x/71x
rity mechanism allows the user to lock all Flash pages, starting at page 0, by writing a non-0xFF value to
the lock byte. Note that writing a non-0xFF value to the lock byte will lock all pages of FLASH from
reads, writes, and erases, including the page containing the lock byte.
The level of Flash security depends on the Flash access method. The three Flash access methods that
can be restricted are reads, writes, and erases from the C2 debug interface, user firmware executing on
unlocked pages, and user firmware executing on locked pages. Table 20.1 summarizes the Flash security
features of the C8051F70x/71x devices.
Table 20.1. Flash Security Summary
Action
Read, Write or Erase unlocked pages
(except page with Lock Byte)
Read, Write or Erase locked pages
(except page with Lock Byte)
Read or Write page containing Lock Byte
(if no pages are locked)
Read or Write page containing Lock Byte
(if any page is locked)
Read contents of Lock Byte
(if no pages are locked)
Read contents of Lock Byte
(if any page is locked)
Erase page containing Lock Byte
(if no pages are locked)
Erase page containing Lock Byte - Unlock all pages
(if any page is locked)
Lock additional pages
(change '1's to '0's in the Lock Byte)
Unlock individual pages
(change '0's to '1's in the Lock Byte)
Read, Write or Erase Reserved Area
C2 Debug
Interface
Permitted
User Firmware executing from:
an unlocked page a locked page
Permitted
Permitted
Not Permitted FEDR
Permitted
Permitted
Permitted
Permitted
Not Permitted FEDR
Permitted
Permitted
Permitted
Permitted
Not Permitted FEDR
Permitted
Permitted
FEDR
FEDR
Only by C2DE FEDR
FEDR
Not Permitted FEDR
FEDR
Not Permitted FEDR
FEDR
Not Permitted FEDR
FEDR
C2DE - C2 Device Erase (Erases all Flash pages including the page containing the Lock Byte)
FEDR - Not permitted; Causes Flash Error Device Reset (FERROR bit in RSTSRC is '1' after reset)
- All prohibited operations that are performed via the C2 interface are ignored (do not cause device reset).
- Locking any Flash page also locks the page containing the Lock Byte.
- Once written to, the Lock Byte cannot be modified except by performing a C2 Device Erase.
- If user code writes to the Lock Byte, the Lock does not take effect until the next device reset.
20.4. Flash Write and Erase Guidelines
Any system which contains routines which write or erase Flash memory from software involves some risk
that the write or erase routines will execute unintentionally if the CPU is operating outside its specified
operating range of VDD, system clock frequency, or temperature. This accidental execution of Flash modi-
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