I have two identical XBee Pro S1 wire antenna units.
Happily, I’ve managed to get the basics right - I can do a simple “chat” app between two computers over transparent comms.
Eventually I’d like to use the API communications mode, which I understand requires the radios to have the “API” firmware installed… Here is the problem.
When I open up X-CTU, I am not given the option to flash the radios with the API function set.
I was unable to successfully flash the radio with anything other than the “XBP24” modem type. And that modem type does not have any function set for API firmware. I’ve tried downloading the latest updates using the “Download new versions” button (which actually fetched a huge amount of new stuff). But that has not given me any options regarding API firmware for this particular radio type.
So how do I get to use API mode with this pair of radios?
In a related issue, I was also expecting to see some “Coordinator” or “End Device” firmware as well, but the only mention of those I can find in this XBP24 config list is the “CE - Coordinator Enable” setting in the main listing of config items. I actually used that to set up one of them radios as coordinator and the other as end device. The firmware itself is identical on both radios and the transparent comms still seems to work ok. Is that the right way to do it?
I’m a bit confused about this whole thing really and I’m wondering if I’ve managed to fluke this working configuration purely by chance - it’s very unintuitive to me.
Any and all advice gratefully received 
Thanks for reading.