If you recall from the RS-232 section, the command ID for the power control is “A” and “1”, but if you
look at the Pronto HEX format, the command ID can only be one byte. This is why we made the
Command IDs out of “HEX compatible” naming – so that the same data when represented as a byte will
look very familiar. Thus the HEX byte for controlling power via IR is 0xA1.
If you were to open the calculator program in Windows, and enter this number by selection the “Hex” radio
button in scientific view mode – then by clicking the “Bin” radio button the calculator will automatically
convert it from HEX to binary for you:
You get the result of: 1010 0001 as the binary number for A1.
Remember that you must fip the number left-to-right for IR to work correctly, so you would get: 1000 0101
Since we want to turn this control “off”, we look up the value for off and find that it is “0” or 0x30 in HEX.
Since this value is only a byte – it is the only “value” byte we need to transmit. By using the Windows
calculator, we can convert this to binary: 0011 0000 – then flip it from MSB-to-LSB: 0000 1100
So we have two of the three parts needed to make a control command – the third and last byte to transmit in
this case is the checksum. The checksum is easier in IR than it is in RS-232, one simply adds the command
ID byte value and the setting value(s). For power off, this is 0xA1 + 0x30 = 0xD1. We can again use
Calculator to convert the HEX value to binary: 1101 0001 then flip it from MSB-to-LSB: 1000 1011
Now we have the IR command in binary (we’ll show the command parts for reference):
0000 Always “zero” to mark the beginning of the code header
006C Carrier Frequency of 38.38kHz
nnnn Number of “bit bursts” in the transmission
0000 Always “zero” to mark the end of the code header
0064 0064 Start “bit” (beginning of command transmission)
1000 0101 8-bit Command ID of 0xA1
0000 1100 8-bit Value byte 1 of 0x30
1000 1011 8-bit Checksum of 0xD1
0044 0044 Stop “bit” (end of command transmission)
0016 0001 End of defined command string “bit”