Up until today, all of the TV’s we have been getting have used NEC Protocol in their remotes. We had one TV, a JVC LT-19N300, which used a modified version of the NEC Protocol. Instead of the header being 9ms as per the standard, they had decreased the header time to 4.5ms as per the below image.
RC-5 Protocol
Today I got a HiSense LEDN19T28 that uses RC-5 Protocol in the remote. This protocol has some really interesting features.
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5 bit address and 6 bit command length (7 command bits for RC5X)
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Bi-phase coding (aka Manchester coding)
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Carrier frequency of 36kHz
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Constant bit time of 1.778ms (64 cycles of 36 kHz)
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Manufacturer Philips
Below is an image of the Modulation of the Logical ‘1’ and Logical ‘0’
You will see that all the bits are of equal length. Each bit had a total length of 1.778ms. You will also notice that half of the bit is filled with a burst of the 36KHz carrier frequency and the other half of the bit remains idle. A Logical ‘0’ is represented by the burst being in the first half of the bit while a Logical ‘1’ is represented by the burst being in the second half of the bit.
Below is an image of the typical pulse train of an RC-5 message.
The first two bits are the start bits and are always a Logical ‘1’. The third bit is a toggle bit. This bit is inverted every time a button is released and pressed again. The inverting of the third bit is not button specific. For example, if you were to press volume up, the third bit returns a Logical ‘0’. If you were to press channel up, the third bit returns a Logical ‘1’. Now if you were to press volume up again, the third bit will return a Logical ‘0’ again.
RC-5 Pre-defined Commands
Below is a table of the pre-defined commands from Philips
| RC-5 Command |
TV Command |
VCR Command |
| $00 – 0 |
0 |
0 |
| $01 – 1 |
1 |
1 |
| $02 – 2 |
2 |
2 |
| $03 – 3 |
3 |
3 |
| $04 – 4 |
4 |
4 |
| $05 – 5 |
5 |
5 |
| $06 – 6 |
6 |
6 |
| $07 – 7 |
7 |
7 |
| $08 – 8 |
8 |
8 |
| $09 – 9 |
9 |
9 |
| $0A – 10 |
-/– |
-/– |
| $0C – 12 |
Standby |
Standby |
| $0D – 13 |
Mute |
|
| $10 – 16 |
Volume + |
|
| $11 – 17 |
Volume – |
|
| $12 – 18 |
Brightness + |
|
| $13 – 19 |
Brightness – |
|
| $20 – 32 |
Program + |
Program + |
| $21 – 33 |
Program – |
Program – |
| $32 – 50 |
Fast Rewind |
|
| $34 – 52 |
Fast Forward |
|
| $35 – 53 |
Play |
|
| $36 – 54 |
Stop |
|
| $37 – 55 |
Recording |
jaysonmarilli 