
156
EPSON
S1C88409 TECHNICAL MANUAL
CHAPTER 5: PERIPHERAL CIRCUITS AND OPERATION (SVD Circuit)
5.16 SVD (Supply Voltage Detection)
Circuit
5.16.1 Configuration of SVD circuit
The S1C88409 has a built-in SVD (supply voltage
detection) circuit, so that the software can find
when the source voltage lowers. Turning the SVD
circuit ON/OFF and the SVD criteria voltage
setting can be done with software.
Figure 5.16.1.1 shows the configuration of the SVD
circuit.
V
SVD
circuit
Detector output
Data
bus
DD
VSS
SVDDT
SVDON
SVDS1
SVDS0
Criteria voltage
setting circuit
Fig. 5.16.1.1 Configuration of SVD circuit
5.16.2 SVD operation
The SVD circuit compares the criteria voltage set
by software and the supply voltage (VDD–VSS) and
sets its results into the SVDDT latch. By reading
the data of this SVDDT latch, it can be determined
by means of software whether the supply voltage
is normal or has dropped.
The criteria voltage can be set for the 3 types
shown in Table 5.16.2.1 by the SVD register.
Table 5.16.2.1 Criteria voltage setting
SVD1
1
0
SVD0
×
1
0
Criteria voltage
3.4 V
2.8 V
1.9 V
When the SVDON register is set to "1", source
voltage detection by the SVD circuit is executed.
As soon as the SVDON register is reset to "0", the
result is loaded to the SVDDT latch and the SVD
circuit goes OFF.
To obtain a stable detection result, the SVD circuit
must be ON for at least l00 sec. So, to obtain the
SVD detection result, follow the programming
sequence below.
1. Set SVDON to "1"
2. Maintain for 100 sec minimum
3. Set SVDON to "0"
4. Read SVDDT
The SVD operation increases current consumption,
so turn the SVD circuit off when voltage detection
is unnecessary or executing the SLP instruction.