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
control register. It is set to “1” when the input voltage is higher than
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