
43
3819 Group
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
MITSUBISHI MICROCOMPUTERS
ZERO CROSS DETECTION CIRCUIT
The zero cross detection circuit compares the voltage applied to
P4
5
/INT
1
/ZCR pin and V
SS
. The result can be read from the zero
cross detection circuit input bit (bit 7) of the zero cross detection
V
SS
and to “0” when it is lower than V
SS
. The input signal to P4
5
/
INT
1
/ZCR pin can select to either pass through the zero cross de-
tection comparator or not to do.
When using 100 V AC as input signal, insert an external circuit be-
tween it and P4
5
/INT
1
/ZCR pin. Set the input current limiting
resistors used in the external circuit to a value which satisfies the
absolute maximum rating of port P4
5
.
Fig. JE-1 External circuit example for zero cross detection
Fig. JE-3 Block diagram of zero cross detection circuit
Fig. JE-2 Structure of zero cross detection control register
V
CC
R
1
R
2
P4
5
/INT
1
/ZCR
V
SS
100V AC
Zero cross detection ON/OFF selection bit
0 : Without passing through zero cross detection comparator
1 : Passing through zero cross detection comparator
Not used (returns “0” when read)
Noise filter sampling clock selection bits (INT
1
)
b3 b2
0 0 : Not use noise filter
0 1 : f(X
IN
)/64 or f(X
CIN
)/64
1 0 : f(X
IN
)/128 or f(X
CIN
)/128
1 1 : f(X
IN
)/256 or f(X
CIN
)/256
One-sided/both-sided edge detection selection bit
0 : One-sided edge detection
1 : Both-sided edge detection
Not used (return “0” when read)
Zero cross detection circuit input bit (read only)
0 : Less than 0 V
1 : 0 V or more
b7
Zero cross detection control register
(ZCRCON : address 0039
16
)
b0
P4
5
/INT
1
/ZCR
Zero cross detection
ON/OFF selection bit
“0”
“1”
Zero cross detection
circuit input bit
Rising/falling
edge switch
Noise filter
When not using
the filter
When using
the filter
INT
1
/ZCR
interrupt request
One-sided/both-sided edge
detection selection bit
Noise filter sampling clock
selection bit
Zero cross detection comparator
f(X
CIN
)
f(X
IN
)
Divider
1/64
1/256
1/28