LC7218, 7218M, 7218JM
Next, the value of the general-purpose counter after the measurement completes must be read out while CTEN is still 1.
(The general-purpose counter is reset when CTEN is set to 0.)
Another point that requires care here is that before starting the general-purpose counter, it must be reset by setting
CTEN to 0.
Note that although signals input to the LCTR pin are transmitted directly to the general-purpose counter, signals input to
the HCTR pin are divided by eight internally before being transmitted to the general-purpose counter. Therefore the
value of the general-purpose counter will be 1/8 of the actual frequency input to the HCTR pin.
When counting intermediate frequency signals, always have the controller first check for the presence of the IF-IC SD
(station detect) signal and then only turn on the IF counter buffer output if the SD signal was present. Auto-search
techniques that only use an IF count are subject to stopping at frequencies where there is no station due to leakage output
from the IF counter buffer.
Note that although the DO pin is forced to the high level when the general-purpose counter is started (when CTEN is set
to 1), the DO pin automatically goes low when the measurement completes (after either 60 or 120 ms has elapsed or
when a signal has been applied for one or two periods). Therefore the DO pin can be used to check for measurement
completion.
1. When the general-purpose is not used (when CTEN is 0) the DO pin can be used to check for changes in external
signals.
• When mode 3 is specified and data is output through DO, DO will automatically go high after data output has
completed, i.e., when CE goes low.
• After that, DO goes low automatically when the IN0 signal changes state.
(That is, DO can be used to check for changes in an external signal input to IN0.)
No. 4758-13/16
SANYO [ SANYO SEMICON DEVICE ]
