Rev. 1.7
99
C8051F330/1/2/3/4/5
Important Note: The VDD monitor must be enabled before it is selected as a reset source. Selecting the
VDD monitor as a reset source before it is enabled and stabilized may cause a system reset. The proce-
dure for configuring the VDD monitor as a reset source is shown below:
Step 1. Enable the VDD monitor (VDMEN bit in VDM0CN = ‘1’).
Step 2. Wait for the VDD monitor to stabilize (see Table 10.1 for the VDD Monitor turn-on time). Step 3. Select the VDD monitor as a reset source (PORSF bit in RSTSRC = ‘1’).
See Figure 10.2 for VDD monitor timing; note that the reset delay is not incurred after a VDD monitor reset. See Table 10.1 for complete electrical characteristics of the VDD monitor. SFR Definition 10.1. VDM0CN: VDD Monitor Control
10.3. 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 10.1 for complete RST pin
specifications. The PINRSF flag (RSTSRC.0) is set on exit from an external reset.
10.4. 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 s, 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.
Bit7:
VDMEN: VDD Monitor Enable.
This bit turns the VDD monitor circuit on/off. The VDD Monitor cannot generate system resets
Monitor must be allowed to stabilize before it is selected as a reset source.
Selecting the
VDD monitor as a reset source before it has stabilized may generate a system reset.
See Table 10.1 for the minimum VDD Monitor turn-on time. 0: VDD Monitor Disabled.
1: VDD Monitor Enabled.
Bit6:
VDD STAT: VDD Status.
This bit indicates the current power supply status (VDD Monitor output).
0: VDD is at or below the VDD monitor threshold.
1: VDD is above the VDD monitor threshold.
Bits5–0: Reserved. Read = 000000b. Write = don’t care.
R/W
R
RRR
R
Reset Value
VDMEN
VDDSTAT Reserved Reserved Reserved Reserved Reserved Reserved
Variable
Bit7
Bit6
Bit5
Bit4
Bit3
Bit2
Bit1
Bit0
SFR Address:
0xFF