document new state behaviours for OFF and CDU

diff --git a/cebpic/README.protocol b/cebpic/README.protocol
index db21ad65eaa5b63690ce654c3b39acf0806174d2..df31395c25d08045bf0ff54cc05282694f8f2360 100644 (file)
--- a/cebpic/README.protocol
+++ b/cebpic/README.protocol
@@ -126,6 +126,11 @@ should be reenabled when the host transmits ON.
                                      (User Fault indicator lit)
 
 
+If OFF is issued in the first 500ms following a short circuit, it will
+be ignored; if the short circuit persists, OFF during the following
+period will go to the `Track and CDU disabled' state without sending
+FIXED.
+
 
 POINTS and CDU
 --------------
@@ -155,6 +160,10 @@ not check that the received P value is 0; they may simply assume it).
        is recharging  <----POINTED----  Point is changing
 
 
+Note that OFF will turn the CDU off, and a short circuit (FAULT) will
+turn it off 500ms later (this delay avoids losing races where the host
+sends a point change instruction just before a short happens).
+
 
 PING and PONG
 -------------