diff -r b930440af354 -r de9122b5680a HP3562A/__init__.py
--- a/HP3562A/__init__.py	Tue Dec 18 00:38:33 2007 +0100
+++ b/HP3562A/__init__.py	Wed Dec 19 00:19:25 2007 +0100
@@ -15,27 +15,46 @@
 import struct
 import re
 import gpib
+import numpy
 
 ########################################
 # HP3562A internal binary types decoders
 
 def decode_float(s):
-    assert len(s) in [4,8]
-    # exponential term 
-    e = ord(s[-1])
-    if e & 0x80:
-        e = e - 256
+    if len(s) == 4:
+        i1, i2, e = struct.unpack('>hbb', s)
+        i2 = i2 * 2**(-23)
+        return (i1/32768. + i2)*2**e
+    else:
+        i1, i2, i3, i4, e = struct.unpack('>hhhbb', s)
+        if i2 < 0:
+            i2 = (i2+32768.)*2**(-15)
+        else:
+            i2 = i2*2**(-15)
+        if i3 < 0:
+            i3 = (i3+32768.)*2**(-30)
+        else:
+            i3 = i3*2**(-15)
+        i4 = i4 * 2**(-38)
+        return (i1+i2+i3+i4)*2**(e-15)
+        
+# def decode_float(s):
+#     assert len(s) in [4,8]
+#     # exponential term 
+#     e = ord(s[-1])
+#     if e & 0x80:
+#         e = e - 256
 
-    # mantissa
-    m = [ord(x) for x in s[:-1]]
-    M = 0.
-    for i in range(len(s)-1):
-        #M += m[i]<<(i*8)
-        M += float(m[i])/2**((i+1)*8)
-    # XXX how do we deal negative numbers?
-    #if m[0] & 0x80:
-    #    M = M - 2^(len(s))
-    return M * 2**(e+1)
+#     # mantissa
+#     m = [ord(x) for x in s[:-1]]
+#     M = 0.
+#     for i in range(len(s)-1):
+#         #M += m[i]<<(i*8)
+#         M += float(m[i])/2**((i+1)*8)
+#     # XXX how do we deal negative numbers?
+#     #if m[0] & 0x80:
+#     #    M = M - 2^(len(s))
+#     return M * 2**(e+1)
 
 def decode_string(s):
     nb = ord(s[0])
@@ -59,6 +78,8 @@
     for row in head_struct:
         key = row[0]
         typ = row[1]
+        if typ is None:
+            continue
         val = header.get(key, "N/A")
         if isinstance(val, basestring):
             val = repr(val)
@@ -83,23 +104,31 @@
     fmt = "%%-%ds %%-%ds"%(maxk, maxv)
     w = maxk+maxv+4
     ncols = columns/w
-    nrows = len(todisp)/ncols
+    if ncols:
+        nrows = len(todisp)/ncols
+    else:
+        nrows = len(todisp)
     res = ""
     for i in range(nrows):
         res += "| ".join([fmt%todisp[j*nrows+i] for j in range(ncols)]) + "\n"
     return res
 
-def decode_header(data, header_struct):    
+def decode_header(data, header_struct, idx=0):    
     d = data
-    typ = d[:2]
-    assert typ == "#A"
-
-    totlen = struct.unpack('>h', d[2:4])[0]
-    idx = 4
+    if d[idx:].startswith('#'):
+        # we have a preliminary header here...
+        typ = d[idx:idx+2]
+        assert typ == "#A"
+        idx += 2
+        totlen = struct.unpack('>h', d[idx:idx+2])[0]
+        idx += 2
     tt=0
     header = {}
     for i, (nam, dtype, fmt, nbytes) in enumerate(header_struct):
-        if dtype == str:
+        if dtype is None:
+            idx += nbytes
+            continue
+        elif dtype == str:
             val = decode_string(d[idx:])
         else:
             if fmt:
@@ -114,6 +143,14 @@
         idx += nbytes
     return header, idx
 
+def read_trace(data, idx, nelts):
+    assert len(data[idx:]) >= (nelts*4), "data[idx:] is too small (%s for %s)"%(len(data[idx:]), (nelts*4))
+    resu = []
+    for i in range(nelts):
+        resu.append(decode_float(data[idx: idx+4]))
+        idx += 4
+    return numpy.array(resu, dtype=float)
+    
 #####################
 # HP3562A constants