Specifications

Remote Control and Receiver-Transceiver Specifications and Requirements
for Windows Media Center in Windows Operating Systems
88
Description
This command sets the IR carrier frequency to use for transmitting IR. The frequency is sent as a
carrier period and a carrier prescalar. The need to use a period value and a prescalar value is
based on the PIC18F4320 timer architecture and maps directly to timer registers in this chip.
CP contains a prescalar value, and CC contains the carrier period in 1/10 μsec steps. The actual
carrier period will be:
Period = ( 2 ^ (CP*2) ) * (CC+1) * 0.1us
where
frequency = 1 / period
Setting CP and CC to 0 will cause the device to use no carrier at all (that is, no light modulation,
just constant on and off periods). The period count value CC can be any number from 0 to 255.
The following table describes CP and CC values for periods from 16 μsec to 34 μsec. This covers
the required range of 30 to 60 KHz. Initial values of CP and CC should be 1 and 66 (37037 Hz),
respectively.
Note This table calculates CP and CC based on periods in whole μsec increments. Because the
table starts with carrier period, which is an integer, and produces CP and CC, which are also
integers, values must be rounded. However, the rounding errors introduced into this table are not
significant enough to affect the accuracy of IR blasting.
Period (μsec)
Carrier (Hz)
CP (μsec)
CC (μsec)
2
500000
0
19
3
333333
0
29
4
250000
0
39
5
200000
0
49
6
166666
0
59
7
142857
0
69
8
125000
0
79
9
111111
0
89
10
100000
0
99
11
90909
0
109
12
83333
0
119
13
76923
0
129
14
71428
0
139
15
66666
0
149