[Elecraft] KPA500 serial interfaces

[Don Wilhelm]

Andy,

You are dealing with an RS-232 communications protocol, which is only 
point to point and not multipoint like Ethernet.

I have no idea how your "polling" device works, but with RS-232, there 
is no polling, it is direct "handshaking" between 2 devices, a DTE and a 
DCE.  If handshaking is implemented, Data Terminal Ready, Data Set Ready 
are exchanged, then Request to Send and the Clear To Send Response are 
sent.  That signalling protocol is normally used only by modems.

Most ham applications do not use those handshaking signals, but rely 
only on Transmit Data and Receive Data to establish communications.

For RS-232 there MUST be only one transmitter - there can be multiple 
receivers, but those devices (other than the main one, either the PC or 
the KPA500) can be the transmitter.  It takes some complex hardware 
device to switch an RS-232 bus from one transmitter to another.

This is a hardware consideration and has nothing to do with software 
such as OmniRig.

Consider the RS-232 voltage levels and you will see why there can be 
only one transmitter on a line.  The active level is between +3.5 volts 
and +25 volts while the inactive level can be from -3.5 volts to -25 volts.
Think about what happens when you connect one device producing +25 volts 
directly to the output of another device producing -25 volts!  That is 
why only one transmitter can be used on an RS-232 signal line.

There are several devices that can be used (such as the SteppIR 
controller) in an RS-232 environment, but their configuration must be 
set to only listen to the traffic on the main RS-232 communications 
which is normally the PC and the transceiver.

The S-Box has the transmitters hardware disabled for all but one port - 
that is how it allows multiple devices to listen in on the communications.

73,
Don W3FPR

On 2/11/2019 3:04 PM, Andy Durbin wrote:
> 
>   "The Serial Box<https://bit.ly/S-BOX> (S-BOX) was specifically designed to make it easy to connect multiple devices in parallel to any transceiver's serial port, including a PC, KPA500, KAT500, KPA1500, SteppIR Controller, Kessler AT-Auto, Shackmaster SM-8, etc. "
> 
> My configuration requires one device to be the routine polling device but has to allow for another device to break that polling interface and insert different commands to the destination equipment.
> 
> E.g - 1. OmniRig polls my TS-590 and my TS-590/Elecraft interface listens to the responses.  When I want to set the TS-590 power, or initiate a TX Tune, my TS-590/Elecraft interface disconnects OmniRig, attaches the local RS232 source, sends the power command, then returns control to OmniRig.    The supplemental commands are timed to only be sent in the "window" where OmniRig is not sending a command.  (It's actually a bit more complicated than that because initiating a TX Tune first inhibits the amplifier key line then, when key inhibit is confirmed, it initiates TX Tune with a specific power setting,  returns TS-590 to receive mode, waits until RX mode is confirmed, then re-enables the amplifier key line.)
> 
> E.g -2.  The KAT500 utility may be polling my KAT500 but I disconnect it and send the KAT500 commands to change L, C, bypass, antenna side, etc.  Again this is is done without disrupting KAT500 utility polling as the commands are only sent in the "window" between the utility polls.   Depending on an option setting the TS-590/Elecraft interface can be the primary KAT500 polling device and the utility is not needed.
> 
> Examples 1 and 2 were implemented a while ago and are mature and reliable.  The next step is to integrate the KPA500 so OPER/STBY are fully integrated in my power control scheme.
>