When you say you got boards what do you mean? Do you mean Sierra development boards with BX31 mounted or your own boards? Assuming it is a BX dev board and you are getting the READY out there is no reason you should not be able to send commands to the unit (assuming GPIO 27 is not connected and you are using an appropriate terminal program). Note the unit does not have echo turned on so you will only see the responses to any commands you send to it and not the actual command itself unless the terminal program has local echo turned on.