Is EXCH instruction still available in-spite of communication function blocks (READ_VAR and WRITE_VAR) in SoMachine Basic.
Yes EXCH instruction is still available. The READ_VAR and WRITE_VAR is implemented just to provide easy user program interface.
You can use both the instruction simultaneously in one application its just like programming of send and receive message. There is no difference function wise the only difference is the programming instruction where you have to write multiple operate instruction for EXCH and design your own message frame but for READ_VAR you just need to put first address and number of register only.
As far as simultaneous execution of instruction is concern you need to take care the only one instruction should be executed at a time for one communication channel or port.