|
...Continued from Page 2.
IR Codes
The world of IR remotes has become a commodity world. IR remotes (simple ones, not the Pronto) are relatively inexpensive. I bought 5, credit card sized, universal remotes for $10. They are three times as thick as a credit card but the same height and width. Fits nicely in a shirt pocket. (A true couch potato must NEVER EVER be without a remote!).
This has happened because there has been a large degree of standardization on the chips that generate the IR codes and receive them. In fact there are only about 5 or 6 such chips being used. Sony, Sharp, Toshiba, Philips and NEC are the most popular, with the NEC one being the most popular of all. The majority of the Asian rim manufacturers (except for Sony, Sharp, Toshiba, and Philips) use NEC chips and therefor NEC format.
I will discuss the exact coding of two of these systems, Sony and NEC. I believe Pioneer, Onkyo, Akai, Canon, Goldstar, Hitachi, Kenwood, NEC, Teac, and Yamaha all use the NEC chip.
[Note: IR data is always transmitted least significant bit first so the first data bit sent is lowest order and in a real binary representation it would be the rightmost bit having a weight of 1.]
SONY IR CODING
ParameterCarrier Frequency
Unit of Burst Time
Lead In Burst
"1" Burst Pattern
"0" Burst Pattern
Lead Out |
Decimal Value40kHz
25 cycles of the carrier
96 24
48 24
24 24
X, 1024 |
HEX Value
0060 0018
0030 0018
0018 0018
0018 03f6 or 0030 03f6 |
The lead out pattern in the Sony code is added to the last bit by increasing the off time. It is NOT a separate burst of data.
Sony data consists of a different number of bits in the message. The first seven bits (the first seven burst pairs after the lead in burst) always represent the key pressed on the remote. The next N bits where in is 5, 8, or 13 represents a device code. Older Sony devices like a TV (no matter what its true model age, it is a device made by Sony for a long time so it is "old") uses a 12 bit code. A newer one like the DVD S7000 uses a 20 bit code. Some remotes can control more than 1 device so they can send codes of different lengths.
Here is an example from a Sony DVD S7000 as it appears in the ProntoEdit Hex Display
0000 0067 0000 0015 0060 0018 0018 0018 0030 0018
0030 0018 0030 0018 0018 0018 0030 0018 0018 0018
0018 0018 0030 0018 0018 0018 0030 0018 0030 0018
0030 0018 0018 0018 0018 0018 0030 0018 0018 0018
0018 0018 0030 0018 0018 03f6
Let us break it up to decipher it.
| Preamble | 0000 0067 000 0015 |
| Word 1 | 0 so it is a learned IR code |
| Word 2 | 103 decimal which when plugged into the formula already given yields an IR Carrier frequency of about 40kHz. |
| Word 3 | 0000 is the length of the One Time Burst. There is no one time burst |
| Word 4 | Decimal 21 is the length of the repeat burst. There are 21 bits (Burst pairs) in this code. The code length is 20 bits plus 1 more pair for the Lead in. |
Word 5,6 |
0060 0018 (96,24 decimal) The lead in Burst . 4 units of on followed by 1 unit of off, where a unit is 600 microseconds |
Word 7,8 |
0018 0018 (24,24 decimal) Burst pair 1, bit 1 = "0" |
| Word 9,10 | 0030 0018 (48,24 decimal) Burst Pair 2, bit 2 = "1" |
| Word 11,12 | 0030 0018 (48,24 decimal) Burst Pair 3, bit 3 = "1" |
| Word 13,14 | 0030 0018 (48,24 decimal) Burst Pair 4, bit 4 = "1" |
| Word 15,16 | 0018 0018 (24,24 decimal) Burst Pair 5, bit 5 = "0" |
| Word 17,18 | 0030 0018 (48,24 decimal) Burst Pair 6, bit 6 = "1" |
| Word 19,20 | 0018 0018 (24,24 decimal) Burst Pair 7, bit 7 = "0" |
The above is the function code as transmitted it is 0111010. Reversing the string so it is a true binary number with the least significant digit on the right we get 0101110 which in decimal is 46.
Continuing on to the device code we have:
| Word 21,22 | 0018 0018 (24,24 decimal) Burst Pair 8, bit 1 = "0" |
| Word 23,24 | 0030 0018 (48,24 decimal) Burst Pair 9, bit 2 = "1" |
| Word 25,26 | 0018 0018 (24,24 decimal) Burst Pair 10, bit 3 = "0" |
| Word 27,28 | 0030 0018 (48,24 decimal) Burst Pair 11, bit 4 = "1" |
| Word 29,30 | 0030 0018 (48,24 decimal) Burst Pair 12, bit 5 = "1" |
| Word 31,32 | 0030 0018 (48,24 decimal) Burst Pair 13, bit 6 = "1" |
| Word 33,34 | 0018 0018 (24,24 decimal) Burst Pair 14, bit 7 = "0" |
| Word 35,36 | 0018 0018 (24,24 decimal) Burst Pair 15, bit 8 = "0" |
| Word 37,38 | 0030 0018 (48,24 decimal) Burst Pair 16, bit 9 = "1" |
| Word 39,40 | 0018 0018 (24,24 decimal) Burst Pair 17, bit 10 = "0" |
| Word 41,42 | 0018 0018 (24,24 decimal) Burst Pair 18, bit 11 = "0" |
| Word 43,44 | 0030 0018 (48,24 decimal) Burst Pair 19, bit 12 = "1" |
| Word 45,46 | 0018 03fc (24,24 decimal) Burst Pair 20, bit 13 = "0" |
The device code as transmitted is 0101110010010. Reversing the order to make it a binary number we get 0100100111010. Converting it to decimal we get 2362.
This means that the Sony DVD S7000 has a device code of 2362 and this key has a function code of 46. This is the discrete Power ON key. If a Sony device has a discrete Power on Code it is normally 46. Note the dead time on the second half of the last data burst pair. Sony does not use a unique lead out, but rather adds the inter-message minimum time to the last data burst’s off period
Sony codes are fairly simple. Sony builds a lot of power into the IR senders, and good noise rejection in their receivers. They use no redundancy or error checking in the code.
|
|
IR Codes Part 1 
Previous page
