Protocols again? Are we ever done talking about protocols? No not really. And BTW this is really RSS version 2! RSS v1 can be found on my other wordpress blog. This version eliminates most of special hardware and its bus and chassis. Most radios heads can be handled by a Arduino Mega256 as it will handle two radios or that is one radio head. If the Mega256 can't handle the job I can then use the Stellaris Launchpad from TI.
We will use one of my Gables G-3717 Dual Nav Head as the guinea pig. 
- Does this radio head have more than one radio? YES
- If yes, how many radios are in this head? 2
- What type of radio head is this? ARINC-410
- Do we have a pin-out? YES
As you can see from the pictures and the table on the right we need ether 5 ASCII letters or 2 ½ bytes for packed format. We also need to label each radio not the head. So that's another ½ byte for a total of 3 bytes. So why are there 4 bytes? The first is byte is a START signal to the receive side to start looking at the input, and start counting bytes. But wait ARINC-410 is a 2 of 5 code and its LOW ACTIVE! And BTW is 28 volt logic to boot, that's in the aircraft, so we will use 5volts. Well not going to send them low active and we will convert the ARINC-410 to Packed Binary or Packed BCD so we can pack each nibble..
| 2 of 5 Code Table | |||||
| No. | A | B | C | D | E |
| 0 | X | X | |||
| 1 | X | X | |||
| 2 | X | X | |||
| 3 | X | X | |||
| 4 | X | X | |||
| 5 | X | X | |||
| 6 | X | X | |||
| 7 | X | X | |||
| 8 | X | X | |||
| 9 | X | X | |||
| Slave Transmit | |||
|---|---|---|---|
| Byte 1 | Byte 2 | Byte 3 | Byte 4 |
| FF | 0001 - 0001 | 0000 - 1000 | 0111 - 0101 |
start-byte | 11 | 08 | 75 |
So you can see that the Slave is transmitting what radio #1 (first nibble of Byte 2) is tuned to 108.75 as you can plainly see in the photograph.
Ok so that takes care of the tuning. But what about the other switches. Ok lets make this eazy lets add another byte, making that number 5. And since there are 8 bits in a byte we now have up to eight switches, or by using the whole byte we could have 256 switches, so why don't we just use the 7 low order bits and the MSB the state of the switch so now we have 128 switches and their states. This way we can assign the switches to numbers in a table. So we can safely say that the OFF/ON or Power switch is #1. In the table below bit 7 is the MSB, and the x indicates the state which is a 0 or 1.
| Switch Byte and Table Layout | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| bit 7 | bit 6 | bit 5 | bit 4 | bit 3 | bit 2 | bit 1 | bit 0 | Radio # | Radio Name | Switch Name |
| x | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 1 | NAV | Power |
| x | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 1 | NAV | VOR_TEST |
| x | 0 | 0 | 0 | 0 | 0 | 1 | 1 | 1 | NAV | UP_RIGHT |
| x | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 1 | NAV | DME_STBY |
| x | 0 | 0 | 0 | 0 | 1 | 0 | 1 | 1 | NAV | OVER_RIDE |
So this really takes care of the Slave_410.tx.c this runs on the embedded microprocessor. We sill need Slave_410.rx.c thats so we can comand the radio head to turn off etc.
So this really takes care of the Slave_410.tx.c this runs on the embedded microprocessor for ARINC-410 class of control head.
Keep Tuned in More to Come
~Cris
BTW Next blog is the Linux Side Control
