Programmable Paging Tone Decoder
CMX823
Before an interrupt can be issued on the detection of a valid tone match, the 1st tone decode mode or 2nd
tone decode mode must have been set (Bit 7 or Bit 6 of the GENERAL Register - $33). This tone decode
mode must match the corresponding tone group programmed into Bit 15 or Bit 14 above.
Each tone to be decoded is identified by 14 bits of data, representing the tone
frequency, according to the formula below:
N and R
(Bit 13 to Bit 0)
For SLOW mode:
n = INT (118920 x f
/ f
)
TONE XTAL
r = ((29730 / f
) - (n / (4 x f
XTAL
))) x 119318.1667
TONE
f
= n x f
/ (240 x (495.5 - (r / 2)))
TONE
XTAL
Example: To decode 1000Hz when using the recommended 3.579545MHz Xtal.
n = INT (118920 x 1000 / 3.579545 x 10^6)
=
INT (33.222) = 33 (truncated)
\
N = 0100001 (binary)
r
=
=
=
((29730 / 3.579545 x 10^6) - (33 / (4 x 1000))) x 119318.1667
6.625
6 (truncated)
\
R = 0000110 (binary)
For FAST mode:
n = INT (59460 x f
/ f
)
TONE XTAL
r = ((14865 / f
) - (n / (4 x f
XTAL
))) x 119318.1667
TONE
f
= n x f
/ (120 x (495.5 - r))
TONE
XTAL
Example: To decode 1000Hz when using the recommended 3.579545MHz Xtal.
n = INT (59460 x 1000 / 3.579545 x 10^6)
=
INT (16.611) = 16 (truncated)
\
N = 0010000 (binary)
r
=
=
=
((14865 / 3.579545 x 10^6) - (16 / (4 x 1000))) x 119318.1667
18.227
18 (truncated)
\
R = 0010010 (binary)
ã 2003 CML Microsystems Plc
12
D/823/3
CMLMICRO [ CML MICROCIRCUITS ]
