1) Do you have 40 independent input conductors, one for each bit?
2) Is the data valid on all conductors at the same time?
3) Is there a signal (clock or strobe) which indicates when the data is valid?
4) How do you know when a data bit is valid?
5) Is an 'acknowledge' signal expected to indicate the data was received?
6) Is there only one wire, with the 40 data bits presented sequentially?
7) How do you know when the 40th data bit is valid so that the next word is expected?
8) Is the sequential data arriving at fixed times, or is there an accompanying clock?
9) Are there two wires, named '1' and '0' and you indicate which bit by pressing the correct key?