S912XEG128J2MAA Datasheet, PDF (495/1324 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 11 S12XE Clocks and Reset Generator (S12XECRGV1)
Table 11-16. Reset Summary
Reset Source
COP Watchdog Reset
Local Enable
COPCTL (CR[2:0] nonzero)
11.5.1 Description of Reset Operation
The reset sequence is initiated by any of the following events:
• Low level is detected at the RESET pin (External Reset).
• Power on is detected.
• Low voltage is detected.
• Illegal Address Reset is detected (refer to device MMC information for details).
• COP watchdog times out.
• Clock monitor failure is detected and Self-Clock Mode was disabled (SCME=0).
Upon detection of any reset event, an internal circuit drives the RESET pin low for 128 SYSCLK cycles
(see Figure 11-21). Since entry into reset is asynchronous it does not require a running SYSCLK.
However, the internal reset circuit of the S12XECRG cannot sequence out of current reset condition
without a running SYSCLK. The number of 128 SYSCLK cycles might be increased by n = 3 to 6
additional SYSCLK cycles depending on the internal synchronization latency. After 128+n SYSCLK
cycles the RESET pin is released. The reset generator of the S12XECRG waits for additional 64 SYSCLK
cycles and then samples the RESET pin to determine the originating source. Table 11-17 shows which
vector will be fetched.
Table 11-17. Reset Vector Selection
Sampled RESET Pin Clock Monitor
COP
(64 cycles after release) Reset Pending Reset Pending
Vector Fetch
1
0
0
POR / LVR /
Illegal Address Reset/
External Reset
1
1
X
Clock Monitor Reset
1
0
1
COP Reset
0
X
X
POR / LVR /
Illegal Address Reset/ External Reset
with rise of RESET pin
NOTE
External circuitry connected to the RESET pin should be able to raise the
signal to a valid logic one within 64 SYSCLK cycles after the low drive is
released by the MCU. If this requirement is not adhered to the reset source
will always be recognized as “External Reset” even if the reset was initially
caused by an other reset source.
MC9S12XE-Family Reference Manual Rev. 1.25
Freescale Semiconductor
495