C8051F52X_12 Datasheet, PDF (110/221 Pages) Silicon Laboratories – 8/4/2 kB ISP Flash MCU Family

C8051F52x/F53x
11.3. External Reset
The external RST pin provides a means for external circuitry to force the device into a reset state. Assert-
ing 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 2.8 on page 32 for complete
RST pin specifications. The PINRSF flag (RSTSRC.0) is set on exit from an external reset.
Note: Please refer to Section “20.6. Reset Low Time” on page 212 for restrictions on reset low time in older silicon
revisions A and B.
11.4. Missing Clock Detector Reset
The Missing Clock Detector (MCD) is a one-shot circuit that is triggered by the system clock. If the system
clock remains high or low for more than 100 µs, 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.
11.5. Comparator Reset
Comparator0 can be configured as a reset source by writing a 1 to the C0RSEF flag (RSTSRC.5).
Comparator0 should be enabled and allowed to settle prior to writing to C0RSEF to prevent any turn-on
chatter on the output from generating an unwanted reset. The Comparator0 reset is active-low: if the non-
inverting input voltage (on CP0+) is less than the inverting input voltage (on CP0-), the device is put into
the reset state. After a Comparator0 reset, the C0RSEF flag (RSTSRC.5) will read 1 signifying
Comparator0 as the reset source; otherwise, this bit reads 0. The state of the RST pin is unaffected by this
reset.
11.6. PCA Watchdog Timer Reset
The programmable Watchdog Timer (WDT) function of the Programmable Counter Array (PCA) can be
used to prevent software from running out of control during a system malfunction. The PCA WDT function
can be enabled or disabled by software as described in Section “19.3. Watchdog Timer Mode” on
page 203; the WDT is enabled and clocked by SYSCLK / 12 following any reset. If a system malfunction
prevents user software from updating the WDT, a reset is generated and the WDTRSF bit (RSTSRC.5) is
set to 1. The state of the RST pin is unaffected by this reset.
11.7. 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 targets an address above the Lock Byte address.
 A Flash read is attempted above user code space. This occurs when a MOVC operation targets an
address above the Lock Byte address.
 A program read is attempted above user code space. This occurs when user code attempts to branch
to an address above the Lock Byte address.
 A Flash read, write or erase attempt is restricted due to a Flash security setting (see Section
“12.4. Security Options” on page 117).
 A Flash write or erase is attempted while the V_DD Monitor (VDDMON0) is disabled or not set to its high
threshold setting.
The FERROR bit (RSTSRC.6) is set following a Flash error reset. The state of the RST pin is unaffected by
this reset.
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Rev. 1.4