C8051F326/7 - Silicon Labs

C8051F326/7
7.3. External Reset
The external RST pin provides a means for external circuitry to force the device into a reset state. Asserting
an active-low signal on the RST pin generates a reset; an external pullup and/or decoupling of the RST
pin may be necessary to avoid erroneous noise-induced resets. See Table 7.1 for complete RST pin specifications.
The PINRSF flag (RSTSRC.0) is set on exit from an external reset.
7.4. Missing Clock Detector Reset
The Missing Clock Detector (MCD) is a one-shot circuit that is triggered by the system clock. If more than
100 µs pass between rising edges on the system clock, the one-shot will time out and generate a reset.
After a MCD reset, the MCDRSF flag (RSTSRC.2) will read ‘1’, signifying the MCD as the reset source;
otherwise, this bit reads ‘0’. Writing a ‘1’ to the MCDRSF bit enables the Missing Clock Detector; writing a
‘0’ disables it. The state of the RST pin is unaffected by this reset.
7.5. Flash Error Reset
If a Flash read/write/erase or program read targets an illegal address, a system reset is generated. This
may occur due to any of the following:
• A Flash write or erase is attempted above user code space. This occurs when PSWE is set to ‘1’ and a
MOVX write operation is attempted above address 0x3DFF.
• A Flash read is attempted above user code space. This occurs when a MOVC operation is attempted
above address 0x3DFF.
• A Program read is attempted above user code space. This occurs when user code attempts to branch
to an address above 0x3DFF.
• A Flash read, write or erase attempt is restricted due to a Flash security setting (see Section
“8.3. Security Options” on page 65).
The FERROR bit (RSTSRC.6) is set following a Flash error reset. The state of the RST pin is unaffected by
this reset.
7.6. Software Reset
Software may force a reset by writing a ‘1’ to the SWRSF bit (RSTSRC.4). The SWRSF bit will read ‘1’ following
a software forced reset. The state of the RST pin is unaffected by this reset.
7.7. USB Reset
Writing ‘1’ to the USBRSF bit in register RSTSRC selects USB0 as a reset source. With USB0 selected as
a reset source, a system reset will be generated when either of the following occur:
1. RESET signaling is detected on the USB network. The USB Function Controller (USB0) must
be enabled for RESET signaling to be detected. See Section “12. Universal Serial Bus Controller
(USB0)” on page 87 for information on the USB Function Controller.
2. The voltage on the VBUS pin matches the polarity selected by the VBPOL bit in register
REG0CN. See Section “5. Voltage Regulator (REG0)” on page 31 for details on the VBUS
detection circuit.
The USBRSF bit will read ‘1’ following a USB reset. The state of the RST pin is unaffected by this reset.
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