power consumption in Stop mode, the PLL can be shut down. This must be done explicitly before entering
Stop mode, since there is no automatic mechanism for this. When the PLL is shut down, the 56800E
system clock must be set equal to the oscillator output.
Some applications require the 56800E STOP and WAIT instructions to be disabled. To disable those
instructions, write to the SIM control register (SIM_CONTROL), described in Part 6.5.1. This procedure
can be on either a permanent or temporary basis. Permanently assigned applications last only until their
next reset.
6.9 Resets
The SIM supports four sources of reset. The two asynchronous sources are the external RESET pin and
the Power-On Reset (POR). The two synchronous sources are the software reset, which is generated within
the SIM itself by writing to the SIM_CONTROL register, and the COP reset.
Reset begins with the assertion of any of the reset sources. Release of reset to various blocks is sequenced
21
to permit proper operation of the device. A POR reset is first extended for 2 clock cycles to permit
stabilization of the clock source, followed by a 32 clock window in which SIM clocking is initiated. It is
then followed by a 32 clock window in which peripherals are released to implement Flash security, and,
finally, followed by a 32 clock window in which the core is initialized. After completion of the described
reset sequence, application code will begin execution.
Resets may be asserted asynchronously, but are always released internally on a rising edge of the system
clock.
Part 7 Security Features
The 56F8355/56F8155 offer security features intended to prevent unauthorized users from reading the
contents of the Flash Memory (FM) array. The Flash security consists of several hardware interlocks that
block the means by which an unauthorized user could gain access to the Flash array.
However, part of the security must lie with the user’s code. An extreme example would be user’s code that
dumps the contents of the internal program, as this code would defeat the purpose of security. At the same
time, the user may also wish to put a “backdoor” in his program. As an example, the user downloads a
security key through the SCI, allowing access to a programming routine that updates parameters stored in
another section of the Flash.
56F8355 Technical Data, Rev. 12
120
Freescale Semiconductor
Preliminary
FREESCALE [ Freescale ]
