--- a/doc/Low-level-commands	Wed Feb 17 18:40:34 2021 +0000
+++ b/doc/Low-level-commands	Wed Feb 17 19:04:00 2021 +0000
@@ -52,8 +52,24 @@
 higher-level fc-simtool commands.
 
 readbin offset len
+
+This fc-simtool command sends a READ BINARY command to the SIM and displays the
+SIM response in raw hex, internally invoking the same function as sim-resp.
+The two arguments are exactly as in the READ BINARY protocol command; each
+number is interpreted as decimal by default or as hex if preceded by 0x.
+
 readrec record-index [len]
 
+This fc-simtool command sends a READ RECORD command to the SIM (absolute
+addressing mode) and displays the SIM response in raw hex, internally invoking
+the same function as sim-resp.  The arguments are decimal or hex as in the
+readbin command.
+
+If no explicit length argument is given, readrec uses the internal variable set
+by the last select operation.  This one-argument form is almost always used in
+practice, as the SIM will normally reject any requested length that does not
+match the current EF record length.
+
 readef
 savebin