SysMLv1: CAUTION: Only a Signal can be used for a SendSignalAction or MessageEvent trigger of an AcceptEventAction, not a Block or ValueType, even if they are valid types for a SysML FlowProperty! But you can "wrap" a Block or ValueType in a Signal.

If you want to use SendSignalAction for exchange items you MUST use a Signal, not a Block or ValueType, for the exchange item, even if SysMLv1 accept any of a Signal, Block, or ValueType as the type of a FlowProperty.

The 'signal' of a SendSignalAction MUST be a Signal. A triggering MessageEvent of an AcceptEventAction MUST (if it isn't an Operation) be a Signal:

However, it you wish to use a Block or ValueType as an exchange item for better integration with your SysMLv1 model, there is way out; just wrap the Block or ValueType as an attribute "packet" of a Signal. You can then receive it on the Pin of an un-marshalled AcceptEventAction or as a Parameter of an effect Activity on a Transition.

It also become tricky when there are families of "packet" types. For example, if a type SubPacket that extends Packet is sent as the "packet", the unmarshalled Pin of an AcceptEventAction for WrapperSignal will be of type Packet, not SubPacket.