RX
-
8025
SA
/
NB
Page - 22 ETM10E-04
8.7.4. Estimation of status based on detection results
The power supply status and clock status can be confirmed by reading the detection results indicated by the PON,
/XST, and VDET bits.
The following are status estimates based on various combinations of detection results.
Address F h
Control 2 Register
Estimated status
bit 4
bit 5
bit 6
Status of power supply and
oscillation circuit
Status of clock and backup
PON
/ XST
VDET
0 0 0
• No supply voltage drop,
but oscillation has
stopped.
• Clock abnormality has occurred → Initialization is
required
∗ Clock has stopped temporarily, possibly due to
condensation.
0 0 1
• Supply voltage has
dropped and oscillation
has stopped.
• Clock abnormality has occurred → Initialization is
required
∗ Clock has stopped, perhaps due to drop in backup
power supply.
0 1 0
• Normal status.
• Normal status.
0 1 1
• Supply voltage has
dropped but oscillation
continues.
• Clock is normal, but an abnormality exists in the power
supply.
∗ Backup power supply may have dropped to a
hazardous level.
1 0
Χ
• Supply voltage has
dropped to 0 V.
• Initialization is required regardless of the clock status
and whether or not a voltage drop has occurred.
∗ Initialization is required due to bits that are reset
when PON = "1".
1 1
Χ
• Power supply flickering is
likely.
∗ The example shown above is when a "1" has already been written to /XST.
32768-
Power-on reset (PON)
Oscillation stop detection
(/XST)
Threshold voltage ( 2.1 V or 1.3 V )
←
0
/XST
1
Supply voltage
PON,VDET
←
0
/XST
1
Internal initialization
PON, VDET
←
0
/XST
1
Internal initialization
Note
When a crystal oscillation is stopping, RX-8035 cannot output ACK signal in I2C access.
Therefore,
In initial-power-ON, please access RX-8035, after crystal oscillation started.
Internal crystal start-up time are 1sec. (Max.)
At initial-power-on, please start access after fixed waiting time.
Or retry repeated access to RX8025 till ACK output from RX8025 with time-out processing.
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