X-Sat / Mitsubishi Protocol

Originally I've called this the X-Sat protocol because it was used in the X-Sat CDTV 310 Satellite receiver made by the French company Xcom. This protocol is probably also used in other X-Sat receivers, but I have no means to verify that.

Update: David Turner informed me that he has seen this protocol being used by Mitsubishi. It could well be that the protocol originally was created by Mitsubishi. I have found a PDF on the internet describing the SC-33B remote control, which is exactly the same protocol. The only difference is that they use a 40kHz carrier, instead of the 38kHz carrier I have seen on the X-Sat receiver.
David also mentioned that he had to transmit each command twice with a 30ms pause between them.

Features

  • 8 bit address and 8 bit command length.
  • Pulse distance modulation.
  • Carrier frequency of 38kHz.
  • Bit time of 1ms or 2ms.

Modulation

X-Sat Modulation

The X-Sat protocol uses pulse distance encoding of the bits. Each pulse is a 526┬Ás long 38kHz carrier burst (about 20 cycles). A logical "1" takes 2.0ms to transmit, while a logical "0" is only 1.0ms. The recommended carrier duty cycle is 1/4 or 1/3.

Protocol

X-Sat Pulse Train

The picture above shows a typical pulse train of the X-Sat protocol. With this protocol the LSB is transmitted first. In this case Address $59 and Command $35 is transmitted. A message is started by a 8ms AGC burst, which was used to set the gain of the earlier IR receivers. This AGC burst is then followed by a 4ms space, which is then followed by the Address and Command. A peculiar property of the X-Sat protocol is the 4ms gap between the address and the command. The total transmission time is variable because the bit times are variable.

X-Sat Repeat Sequence

An IR command is repeated every 60ms for as long as the key on the remote is held down.