lc7219m Sanyo Semiconductor Corporation, lc7219m Datasheet - Page 8

• Manufacturer Part Number: lc7219m
• Description: Pll Frequency Synthesizers
• Manufacturer: Sanyo Semiconductor Corporation

General-purpose Counter
The 20-bit general-purpose counter is used for both frequency and period measurement as shown in figure 8. The
measurement mode is selected by bits SC and SF as shown in table 7. The counter value is output on DO with the msb
first.
Table 7. General-purpose counter mode selection
Note
In frequency measurement mode, the input cycles during a 30 or 60 ms interval are counted. Either LCTR or HCTR
can be selected as the counter input.
In period measurement mode, LCTR is the single input, and the 900kHz cycles in one or two periods of the LCTR
signal are counted.
The counter starts when the CTEN flag is set. The serial input data is latched in on the falling edge of CE. The input
data on HCTR or LCTR should be input within 10 ms of this transition.
The period or frequency measurement count should be read while CTEN is still set to 1, as the counter is reset by
setting CTEN to 0. CTEN should be set to 0 before each measurement.
The LCTR signal is passed directly to the counter input. The HCTR signal is passed through a divide-by-eight
prescaler. The actual HCTR frequency is, therefore, eight times the measured frequency.
When the universal counter is used as the IF counter, the state of the IF-IC SD (station detect) signal must be checked
by the microcontroller, and the IF counter buffer output turned on only after the SD signals are activated. Auto-search
techniques using only the IF counter are not advisable since it is possible that the search can stop incorrectly at a
location that does not have a station due to the IF counter buffer output leakage.
DO goes HIGH when the CTEN flag is set to 1, and LOW when frequency or period measurement is completed. DO
can be monitored to check for measurement completion. The timing for the general-purpose counter is shown in figure
9.
= don’t care
S
1
0
0
C
S
1
0
F
n I
H
p
L
L
t u
C
C
C
T
T
T
p
R
R
R
o
t r
F
F
P
e r
e r
r e
q
q
o i
u
u
d
e
e
n
n
m
y c
y c
e
a
m
m
s
u
e
e
e r
P
a
a
a
s
s
m
a r
u
u
e
e r
e r
m
t n
Figure 8. General-purpose counter
m
m
t e
p (
e
e
r e
t n
t n
u
s l
s (
s (
e
LC7219, 7219M
n i
n i
w
e
e
a
w
w
v
) e
a
a
v
v
) e
) e
No.3661–8/12