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| ITT Protocol |
The ITT IR protocol is a very old one. It differs from other protocols
in that it does not use a modulated carrier frequency to send the IR
messages. A single command is transmitted by a total of 14 pulses with a
width of 10µs each. The command is encoded by the distance between the
pulses.
This protocol is very reliable and consumes very little power
ensuring long battery life.
Many consumer electronics brands used this protocol in Europe. Among them were: ITT, Greatz, Schaub-Lorenz, Finlux, Luxor, Salora, Oceanic and later also Nokia, to name but a few.
| Features |
- Only 14 very short IR pulses per message
- Pulse distance encoding
- Long battery life
- 4 bit address, 6 bit command length
- Self calibrating timing, allowing only simple RC oscillator in the transmitter
- Fast communication, a message takes from 1.7ms to 2.7ms to transmit
- Manufacturer Intermetal, now Micronas
| Protocol |
An IR message is transmitted by sending
14 pulses. Each pulse is 10µs long. Three different time intervals are
used to get the message across: 100µs for a logic 0, 200µs for a logic 1
and 300µs for the lead-in and lead-out.
The preliminary pulse is used by the
receiver to set the gain of the amplifier. Then follows a lead-in delay of
300µs, after which the starting pulse is given. The first bit sent is
always logic 0, which has a delay duration of 100µs. This start bit can be
used to calibrate the timing of the receiver. After the start bit follow 4
bits (MSB first) that represent the address of the message. After that a
total of 6 bits (MSB first) for the command are transmitted. A trailing
pulse should follow this command. Finally another 300µs delay follows
before the very last pulse, functioning as a lead-out.
There are a few things the receiving software can check to verify the
validity of the received message. The lead-out interval should be 3 times
longer than the start bit time, which has a duration of 100µs. Bit times
should not be off by more than ±20% of the start bit length for logic 0s,
or 2x the start bit length for logic 1s.
Don't keep waiting for pulses
after 360µs after the last received pulse. It's very likely that the
transmission is interrupted or no transmission took place at all if you
have to wait longer than that.
The preliminary pulse serves only AGC
purposes and may be ignored by the receiving software. Decoding of the
message should start at the Start pulse.
| Address and Command |
A control message is divided into two groups, an address of 4 bits and a command of 6 bits. Addresses range from 1 to 16, and commands range from 1 to 64. Before the address and command are sent, 1 is subtracted from both values to get them in the range 0 to 15 and 0 to 63.
Addresses are used in pairs. A pair of addresses is a value of 1 to 8
(0 to 7 actually), and it's inverted counter part 16 to 9 (15 to 8
actually).
The lower value address is transmitted the first time a key
is pressed. The address value of all subsequent messages will be the
inverted value of this first address until the key is released. This
enables the receiver to interpret repeat codes properly. Messages are
repeated every 130ms as long as the key remains pressed.
| Transmitter |
Intermetall has developed a few transmitter ICs for use in handsets. Later microcontrollers were used to facilitate the combination of TV, VCR and SAT remote control in one handset.
The SAA1250 was the first IR controller IC to be released. It can be set to generate 3 different address pairs. A fourth option is transmitting any of the 16 addresses. That option is rarely used, for it requires a manual setup procedure every time the power is lost.
The second generation of IR controller ICs are the IRT1250 and IRT1260.
These chips are identical in operation and differ only in the operating
voltage. The IRT1250 is intended for 9V operation, whilst the IRT1260 is
designed for 3V.
The footprint of the IRT12x0 is the same as that of
the SAA1250. The devices differ in addressing capability and current drive
capacity for the output stage.
Two address pins are available to set the address pair used.
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Addresses 1 and 16 are always used to control TV sets. Other address pairs are not always uniquely linked to a particular equipment family.
| Receiver |
The ITT protocol makes no use of a modulated carier, so the previously
mentioned IR receivers won't work for this protocol. Intermetall has
created the TBA2800 for use with this protocol. It is a highly senisive IR
detection circuit and should be shielded completely inside a metal box
that is connected to ground, leaving only a small hole just in front of
the IR diode. 
There is actually not much
more to be told about this IC. Just connect it as shown in the diagram as
shown above, and it should work. You can chose between a normal high going
output, and an inverted low going output. It depends on the rest of your
circuitry which one you should use.
In case of excessive interference
you could reduce the sensitivity a little by grounding pin 6 via a 10k
resistor.
| Pre-defined Commands |
Some of the 64 possible commands are predefined. But unfortunately the definition of the commands is not as clear as with RC-5. You can find most of the pre-defined commands for TV purposes in the following table. TV commands use the address pair 1 and 16.
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