SPA physical layer


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1. Is there a difference between the physical layer of the SPA-rear port on the ABB REF542 and REX 521 relays and the standard RS485?

2. Are the RTS A and RTS B really used ( Note that SPA is a single master with slave unable to initiate conversation; hence, access control is not that necessary)?

3. Finally, can we use programmable RS485 ports on third party devices to access the SPA slaves after implementing the ASCII based SPA communication protocol on the third party device?