Rev. 1.2
123
C8051T620/1/6/7 & C8051T320/1/2/3
the level required for data retention. If the PORSF flag reads 1, the data may no longer be valid. The V
DD
monitor is enabled after power-on resets. Its defined state (enabled/disabled) is not altered by any other
reset source. For example, if the V
DD
monitor is disabled by code and a software reset is performed, the
V
DD
monitor will still be disabled after the reset.
I
mportant Note:
If the V
DD
monitor is being turned on from a disabled state, it should be enabled before it
is selected as a reset source. Selecting the V
DD
monitor as a reset source before it is enabled and stabi-
lized may cause a system reset. In some applications, this reset may be undesirable. If this is not desirable
in the application, a delay should be introduced between enabling the monitor and selecting it as a reset
source. The procedure for enabling the V
DD
monitor and configuring it as a reset source from a disabled
state is shown below:
1. Enable the V
DD
monitor (VDMEN bit in VDM0CN = 1).
2. If necessary, wait for the V
DD
monitor to stabilize (see Table 7.4 for the V
DD
Monitor turn-on time).
3. Select the V
DD
monitor as a reset source (PORSF bit in RSTSRC = 1).
See Figure 20.2 for V
DD
monitor timing; note that the power-on-reset delay is not incurred after a V
DD
monitor reset. See Table 7.4 for complete electrical characteristics of the V
DD
monitor.