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C8051F310 Datasheet, PDF (105/224 Pages) List of Unclassifed Manufacturers – 8/16 kB ISP Flash MCU Family
C8051F310/1/2/3/4/5/6/7
any other reset source. For example, if the VDD monitor is enabled and a software reset is performed, the
VDD monitor will still be enabled after the reset.
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 9.1 for the VDD Monitor turn-on time).
Note: This delay should be omitted if software contains routines that erase or write Flash
memory.
Step 3. Select the VDD monitor as a reset source (PORSF bit in RSTSRC = ‘1’).
See Figure 9.2 for VDD monitor timing; note that the reset delay is not incurred after a VDD monitor reset.
See Table 9.1 for complete electrical characteristics of the VDD monitor.
SFR Definition 9.1. VDM0CN: VDD Monitor Control
R/W
VDMEN
Bit7
R
R
R
R
R
R
R
Reset Value
VDDSTAT Reserved Reserved Reserved Reserved Reserved Reserved Variable
Bit6
Bit5
Bit4
Bit3
Bit2
Bit1
Bit0
SFR Address: 0xFF
Bit7:
Bit6:
Bits5–0:
VDMEN: VDD Monitor Enable.
This bit is turns the VDD monitor circuit on/off. The VDD Monitor cannot generate system
resets until it is also selected as a reset source in register RSTSRC (Figure 9.2). The VDD
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 9.1 for the minimum VDD Monitor turn-on time.
0: VDD Monitor Disabled.
1: VDD Monitor Enabled.
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.
Reserved. Read = Variable. Write = don’t care.
9.3. 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 9.1 for complete RST pin spec-
ifications. The PINRSF flag (RSTSRC.0) is set on exit from an external reset.
Rev. 1.6
105