Using a keypad challenge — control program sends to the swipe-card reader

In the case where Control is sending data to Swipe, in conjunction with a keypad challenge, we have the following steps:

1. Control sends to Swipe.
2. Swipe replies with, OK, event primed.
3. A big delay occurs until the next person swipes their card.
4. Swipe uses a pulse to say, I have data available.
5. Control sends a message, What is your data?
6. Swipe replies with, Swipe card ID # xxxx was swiped.
7. Control sends message, Challenge the user with YYYY.
8. Swipe replies with, OK, challenge in progress.
9. A delay occurs while the user types in the response.
10. Swipe sends a pulse to Control with, Challenge complete. (We're assuming that the challenge response doesn't fit in a pulse.)
11. Control sends a message, What is the challenge response?
12. Swipe replies with, Challenge response is IZZY.
13. Control sends a message, change LED to GREEN.
14. Swipe replies with, OK.
15. A 20-second delay occurs, while the door is opened.
16. Control sends a message, Change LED to RED.
17. Swipe replies with, OK.

In this case, there were two pulses and six messages. Again, the initial priming message could be discounted.