Rx5C348A/B
Oscillation Halt Sensing, and Supply Voltage Monitoring
XSTP and VDET
The oscillation halt sensing circuit is configured to record a halt on oscillation by 32.768-kHz clock pulses. The
supply voltage monitoring circuit is configured to record a drop in supply voltage below a threshold voltage of 2.1
or 1.6v.
Each function has a monitor bit. I.e. XSTP bit is for the oscillation halt sensing circuit, and VDET is for the
supply voltage monitoring circuit. XSTP and VDET bits are activated to “H”. The XSTP and VDET accept only
the writing of 0. The XSTP bit is set to 1, when VDD power-up from 0V, but VDET is set to 0.
The functions of these two monitor bits are shown in the table below.
Oscillation Halt Sensing Circuit operates only when CE pin is Low. Sensing result is maintained after CE pin
changes from “L” to “H”.
XSTP
0
0
1
VDET
0
1
*
Conditions of supply voltage and oscillation
No drop in supply voltage below threshold voltage and no halt in oscillation
Drop in supply voltage below threshold voltage and no halt in oscillation
Halt on oscillation
Threshold voltage (2.1v or 1.6v)
VDD
32768Hz Oscillation
Oscillation halt
sensing flag (XSTP)
Supply voltage
monitor flag (VDET)
VDET←0
XSTP←0
VDET←0
VDET←0
XSTP←0
Internal initialization
period (1 to 2 sec.)
Internal initialization
period (1 to 2 sec.)
When the XSTP bit is set to 1 in the control register 2, the (0), F6 to F0, WALE, DALE, /12⋅24, /CLEN2, TEST,
CT2, CT1, CT0, VDSL, VDET, /CLEN1, CTFG, WAFG, DAFG, SCRATCH1/2/3 bits are reset to 0 in the oscillation
adjustment register, the control register 1, and the control register 2.
< Considerations in Using Oscillation Halt Sensing Circuit >
Be sure to prevent the oscillation halt sensing circuit from malfunctioning by preventing the following:
1) Instantaneous power-down on the VDD
2) Condensation on the crystal oscillator
3) On-board noise to the crystal oscillator
4) Applying to individual pins voltage exceeding their respective maximum ratings
In particular, note that the XSTP bit may fail to be set to 0 in the presence of any applied supply voltage as
illustrated below in such events as backup battery installation. Further, give special considerations to prevent
excessive chattering in the oscillation halt sensing circuit.
VDD
12345
Rev.2.01
- 32 -
RICOH [ RICOH ELECTRONICS DEVICES DIVISION ]
