--- a/docs/extension-virtualports.txt	Sun May 29 21:59:29 2016 -0600
+++ b/docs/extension-virtualports.txt	Sat Jun 11 11:13:49 2016 -0600
@@ -165,3 +165,39 @@
 appropriate.
 
 
+06 VPORT_READFIXED
+
+This request reads bytes from a virtual port. The request looks as follows:
+
+Octet	Meaning
+-----	-------
+0-2	F3 00 04
+3	port number
+4	size to read in octets (N)
+
+The response is looks as follows:
+
+Octet	Meaning
+-----	-------
+0	status
+1	number of bytes returned (n)
+2-...	returned data
+
+In all cases, there will be exactly N octets in the returned data. Any bytes
+not filled by actual data are undefined but should be zero.
+
+If status is nonzero, then the read failed. This will usually be due to a
+lack of data (1) OR the port not being open (2). In this case, any
+subsequent octets in the packet can be ignored.
+
+If (n) is less than (N), then there will be extra octets in the returned
+data section which must be ignored.
+
+This option is provided as an alternative to the VPORT_READ call for systems
+which cannot easily handle a variable length packet safely. In particular, a
+115k "bitbanger" implementation on the Coco itself might choose to use this
+option to adding another 500+ bytes to its lwwire client driver. Ohter
+communication channels that do not have this limitation should prefer the
+variable length packet option with larger request sizes to minimize
+transaction count.
+