Reset Operation; Reset Pins; Reset Sources; Reset Functional Block Diagram - Motorola Freescale Semiconductor M-Core MMC2001 Reference Manual

9.3 Reset Operation

9.3.1 Reset Pins

Three reset related pins are provided on MMC2001: a reset input (RSTIN), a low-volt-
age detect reset input (LVRSTIN), and a reset output (RSTOUT).
The RSTIN input is an active low input which is connected to external power-on and
other reset control sources. This input is qualified as a valid reset if held low for at
least four LOW_REFCLK clock cycles.
The LVRSTIN input is an active low input which is connected to low-voltage detection
circuitry. No qualification is performed for this input; it must thus be driven in a well-
controlled manner.
The RSTOUT output is an active drive pin used to reset external devices. This pin is
driven low when either qualified external resets are detected or on-chip resets
(watchdog timer, power-up-reset circuitry) are generated. The minimum length is
eight LOW_REFCLK cycles. The RSTOUT pin remains low if either reset input pin is
held low.

9.3.2 Reset Sources

Three sources are capable of generating a reset condition:
• An external qualified low condition on either reset input pin. The RSTIN signal
must be valid low for four LOW_REFCLK clock cycles. LVRSTIN has no qualifi-
cation requirements.
• Internal watchdog timer.
• Internal power-on reset circuitry.
LVRSTIN
RSTOUT
LOW_REFCLK
RSTIN
Power-up bypass
MOD
MOTOROLA
9-2
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4-cycle
Qual.
Watchdog
Timer
Reset Status
Register
Figure 9-1 Reset Functional Block Diagram
TIMER/RESET MODULE
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4-cycle
4-cycle
stretcher stretcher
Signal to latch MOD pin
EN
Internal MOD
D Q
signal to EIM
REFERENCE MANUAL
To internal
resets
MMC2001