Xin Oscillation Stoppage Detection Circuit - Renesas M32R/ECU Series User Manual

18

18.1.2 XIN Oscillation Stoppage Detection Circuit

The M32R/ECU contains a detection circuit to find whether oscillation input to the PLL circuit has stopped. The
PLL circuit has a characteristic that in the absence of the reference oscillation input, it oscillates with the fre-
quency of its normal mode of vibration.
The XIN oscillation input is sampled at the multiply-by-n frequency of the PLL circuit and when the XIN oscillation
is found to be at the same level, the XSTAT bit is set. Because the CPU continues operating with the PLL circuit's
natural frequency even when the XIN oscillation has stopped, error handling for the stoppage of XIN oscillation
can be accomplished by inspecting XSTAT in software.
Oscillator
XIN
circuit
Figure 18.1.2 Block Diagram of the XIN Oscillation Stoppage Detection Circuit
Port Input Special Function Control Register (PICNT)
b8 9 10
0 0 0
b Bit Name
8–10 No function assigned. Fix to "0".
11 XSTAT
XIN oscillation status bit
12–13 No function assigned. Fix to "0".
14 PISEL
Port input data select bit
15 PIEN0
Port input enable bit
Note 1: Only writing "0" is effective. Writing "1" has no effect; the bit retains the value it had before the write.
For details about the function of the port input data select bit (PISEL) and port input enable bit (PIEN0), see Section
8.3.5, "Port Input Special Function Control Register."
PLL circuit
11 12 13 14
XSTAT PISEL
0 0 0 0
Counter
XIN oscillation stoppage detection circuit
b15
PIEN0
0
Function
0: XIN oscillating
1: XIN inactive
0: Content of port output latch
1: Port pin level
0: Disable input
1: Enable input
18-3
OSCILLATOR CIRCUIT
18.1 Oscillator Circuit
XSTAT
Determination
circuit
flag
<Address: H'0080 0745>
<After reset: H'00>
32180 Group User's Manual (Rev.1.0)
R W
0 0
R (Note1)
0 0
R W
R W