Controlling Protocol ......
“Read Rx Tone Frequency Register”
– A/C 32
H
, followed by 2 bytes of Reply Data.
Measurement of Rx Signal Frequency (S
INPUT
)
The measurement details given on Pages 10 and 11 are
for a Xtal/clock frequency (f
XTAL
) of 4.032MHz, a scaling
formula for other values of f
XTAL
is given at the bottom of this
page.
The input audio signal (S
INPUT
) is filtered and measured in
the Frequency Counter over a specified “measurement
period” (9.125 ms or 18.250 ms).
The measuring function counts the number of complete
input cycles occurring within the measurement period and
then the number of measuring-clock cycles necessary to
make up the period.
When the count period of a successful decode is
complete, the Rx Tone Measurement bit in the Status
Register, and the Interrupt bit (if enabled) are set.
The Rx Tone Frequency Register will now indicate the
signal frequency (S
INPUT
) in the form of 2 bytes (1 and 0) as
illustrated in Figure 6 below.
Measurement Period
Complete
Input
Cycle
Complete
Input
Cycle
Complete
Input
Cycle
Complete
Input
Cycle
Complete Measuring
Clock
Input
Cycles
Cycle
FILTERED AUDIO INPUT SIGNAL 2 x
S
INPUT
N
Fig.5 Measurement of a Mid or High Band Rx Frequency
R
The Integer (N)
– Byte 1
A binary number representing
‘twice the number of
complete input audio cycle periods’
counted during the
specified measurement period, which is:
High Band Decode
Mid Band Decode
Extended Band Decode
=
=
=
9.125 ms
18.250 ms
9.125 ms
=
=
=
“t”
“t”
“t”
The Remainder (R)
– Byte 0
A binary number representing the remainder part, R,
of 2 x Input Signal Frequency (S
INPUT)
.
‘R = number of
specified measuring-clock cycles’
required to complete the
specified measurement period (See N).
The clock-cycle frequencies are:
High Band Decode
= 56.00 kHz
Mid Band Decode
= 28.00 kHz
Extended Band Decode
= 56.00 kHz
See the bottom of this page for “t” and “f” scaling factors
=
=
=
“f”
“f”
“f”
(REPLY DATA)
(MSB) – TRANSMITTED FIRST
Byte 1
12
11
10
9
8
7
6
5
Byte 0
4
3
(REPLY DATA)
(LSB) – TRANSMITTED LAST
15
14
13
2
1
0
“0” “0”
Integer (N)
“0” “0”
Remainder (R)
Fig.6 Format of the Rx Tone Frequency Register
f
XTAL
Scaling Factors
The calculations above are for an f
XTAL
of 4.032MHz. The
following formulas enable the calculation of these values
using any Xtal value. Note: f
XTAL
values are stated in MHz.
“t”
scaled
“f”
scaled
=
“t” x
4.032
f
XTAL
f
XTAL
4.032
=
“f” x
8
CMLMICRO [ CML MICROCIRCUITS ]
