diff --git a/doc/source/firmware.rst b/doc/source/firmware.rst
index 2f3eb88da5eb7e7eeb4d56398b8841159a4b75b2..fc67ab897e311e4f747545e45211dbf631bef4cd 100644
--- a/doc/source/firmware.rst
+++ b/doc/source/firmware.rst
@@ -174,7 +174,9 @@ PAGE
 
 The PAGE command is used to select a power rail for the READ_VOUT,
 READ_IOUT and READ_POUT commands. Allowed values for the page
-parameter are :math:`0 \leq N \leq 2`.
+parameter are :math:`0 \leq N \leq 3` for the DI/OT Rad-Tol System
+Board revision and :math:`0 \leq N \leq 2` for the fan-tray, RaToPUS
+and generic prototype revisions.
 
 QUERY
 ~~~~~