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 turn on the IF counter buffer output only when the SD signal is present. Auto-search

techniques that use an IF count only 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 24 or 12 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.

Comparison of counting times

Notes:* The value of the coupling capacitor must be under 1000 pF, since this product has a shorter wait time than the other products.

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.

No. 3985-13/16

LC72191, 72191M, 72191JM

Catatog no.

Measurement time (tG)

Wait time (tW)

GT = 0

GT = 1

LC72191/M/JM

12 ms

24 ms

2 to 3 ms*

LC7219/M

60 ms

30 ms

10 to 15 ms

LC7218/M/JM

60 ms

120 ms

10 to 15 ms