diff --git a/scapy/contrib/pnio.uts b/scapy/contrib/pnio.uts
index 979ed70a6..906b46f0b 100644
--- a/scapy/contrib/pnio.uts
+++ b/scapy/contrib/pnio.uts
@@ -8,7 +8,7 @@ from scapy.contrib.pnio import *
 + Check DCE/RPC layer
 
 = ProfinetIO default values
-str(ProfinetIO()) == b'\x00\x00'
+raw(ProfinetIO()) == b'\x00\x00'
 
 = ProfinetIO overloads Ethertype
 p = Ether() / ProfinetIO()
@@ -19,14 +19,14 @@ p = UDP() / ProfinetIO()
 p.dport == 0x8892
 
 = Ether guesses ProfinetIO as payload class
-p = Ether('ffffffffffff00000000000088920102'.decode('hex'))
+p = Ether(hex_bytes('ffffffffffff00000000000088920102'))
 p.payload.__class__ == ProfinetIO and p.frameID == 0x0102
 
 = UDP guesses ProfinetIO as payload class
-p = UDP('12348892000a00000102'.decode('hex'))
+p = UDP(hex_bytes('12348892000a00000102'))
 p.payload.__class__ == ProfinetIO and p.frameID == 0x0102
 
 = ProfinetIO guess payload to PNIORealTime
-p = UDP('12348892000c000080020102'.decode('hex'))
+p = UDP(hex_bytes('12348892000c000080020102'))
 p.payload.payload.__class__.__name__ == 'PNIORealTime' and p.frameID == 0x8002
 
diff --git a/scapy/contrib/pnio_rtc.py b/scapy/contrib/pnio_rtc.py
index 0a9714be3..d9533c7f5 100644
--- a/scapy/contrib/pnio_rtc.py
+++ b/scapy/contrib/pnio_rtc.py
@@ -36,6 +36,7 @@ from scapy.fields import BitEnumField, BitField, ByteField,\
 
 # local imports
 from scapy.contrib.pnio import ProfinetIO
+from scapy.compat import orb
 from scapy.modules.six.moves import range
 
 
@@ -226,13 +227,13 @@ class PNIORealTime(Packet):
         # dissected packets
         pkt_len = self.getfieldval("len")
         if pkt_len is not None:
-            return max(0, pkt_len - len(fld.addfield(self, "", val)) - 4)
+            return max(0, pkt_len - len(fld.addfield(self, b"", val)) - 4)
 
         if isinstance(self.underlayer, ProfinetIO) and \
                 isinstance(self.underlayer.underlayer, UDP):
-            return max(0, 12 - len(fld.addfield(self, "", val)))
+            return max(0, 12 - len(fld.addfield(self, b"", val)))
         else:
-            return max(0, 40 - len(fld.addfield(self, "", val)))
+            return max(0, 40 - len(fld.addfield(self, b"", val)))
 
     @staticmethod
     def analyse_data(packets):
@@ -265,7 +266,7 @@ class PNIORealTime(Packet):
                     counts.extend([0 for _ in range(len(pdu) - len(counts))])
 
                 for i in range(len(pdu)):
-                    if pdu[i] != b"\x80":
+                    if orb(pdu[i]) != 0x80:
                         counts[i] += 1
 
                 comm = (pkt.src, pkt.dst)
@@ -279,7 +280,7 @@ class PNIORealTime(Packet):
             loc = locations[comm] = []
             start = None
             for i in range(length):
-                if counts[i] > total / 2:   # Data if more than half is != 0x80
+                if counts[i] > total // 2:   # Data if more than half is != 0x80
                     if start is None:
                         start = i
                 else:
@@ -421,7 +422,7 @@ def entropy_of_byte(packets, position):
     # Count each byte a appearance
     for pkt in packets:
         if -position <= len(pkt):     # position must be a negative index
-            counter[ord(pkt[position])] += 1
+            counter[orb(pkt[position])] += 1
 
     # Compute the Shannon entropy
     entropy = 0
diff --git a/scapy/contrib/pnio_rtc.uts b/scapy/contrib/pnio_rtc.uts
index 7c8934b21..43b4b18c5 100644
--- a/scapy/contrib/pnio_rtc.uts
+++ b/scapy/contrib/pnio_rtc.uts
@@ -9,7 +9,7 @@ from scapy.contrib.pnio_rtc import *
 + Check PNIORealTimeIOxS
 
 = PNIORealTimeIOxS default values
-str(PNIORealTimeIOxS()) == b'\x80'
+raw(PNIORealTimeIOxS()) == b'\x80'
 
 = Check no payload is dissected (only padding)
 * In order for the PNIORealTime to dissect correctly all the data buffer, data field must strictly dissect what they know as being of themselves
@@ -20,69 +20,69 @@ p == PNIORealTimeIOxS(dataState='bad', instance='device') / conf.padding_layer(b
 + Check PNIORealTimeRawData
 
 = PNIORealTimeRawData default values
-str(PNIORealTimeRawData(config={'length': 5})) == b'\x00\x00\x00\x00\x00'
+raw(PNIORealTimeRawData(config={'length': 5})) == b'\x00\x00\x00\x00\x00'
 
 = PNIORealTimeRawData must always be the same configured length
-str(PNIORealTimeRawData(load='ABC', config={'length': 5})) == b'ABC\x00\x00'
+raw(PNIORealTimeRawData(load='ABC', config={'length': 5})) == b'ABC\x00\x00'
 
 = PNIORealTimeRawData may be truncated
-str(PNIORealTimeRawData(load='ABCDEF', config={'length': 5})) == 'ABCDE'
+raw(PNIORealTimeRawData(load='ABCDEF', config={'length': 5})) == b'ABCDE'
 
 = Check that the dissected payload is an PNIORealTimeIOxS (IOPS)
 p = PNIORealTimeRawData(b'ABCDE\x80\x01\x02', config={'length': 5})
-p == PNIORealTimeRawData(load='ABCDE', config={'length': 5}) / PNIORealTimeIOxS() / conf.padding_layer(b'\x01\x02')
+p == PNIORealTimeRawData(load=b'ABCDE', config={'length': 5}) / PNIORealTimeIOxS() / conf.padding_layer(b'\x01\x02')
 
 = PNIORealTimeRawData is capable of dissected uncomplete packets
 p = PNIORealTimeRawData('ABC', config={'length': 5})
-p == PNIORealTimeRawData(load='ABC', config={'length': 5})
+p == PNIORealTimeRawData(load=b'ABC', config={'length': 5})
 
 
 + Check Profisafe
 
 = Profisafe default values
-str(Profisafe(config={'length': 7, 'CRC': 3})) == b'\0\0\0\0\0\0\0'
+raw(Profisafe(config={'length': 7, 'CRC': 3})) == b'\0\0\0\0\0\0\0'
 
 = Profisafe must always be the same configured length
-str(Profisafe(load='AB', config={'length': 7, 'CRC': 3})) == b'AB\0\0\0\0\0'
+raw(Profisafe(load=b'AB', config={'length': 7, 'CRC': 3})) == b'AB\0\0\0\0\0'
 
 = Profisafe load may be truncated
-str(Profisafe(load='ABCDEF', config={'length': 7, 'CRC': 3})) == b'ABC\0\0\0\0'
+raw(Profisafe(load=b'ABCDEF', config={'length': 7, 'CRC': 3})) == b'ABC\0\0\0\0'
 
 = Check that the dissected payload is an PNIORealTimeIOxS (IOPS)
 p = Profisafe(b'ABC\x20\x12\x34\x56\x80\x01\x02', config={'length': 7, 'CRC': 3})
-p == Profisafe(load='ABC', Control_Status=0x20, CRC=0x123456, config={'length': 7, 'CRC': 3}) / PNIORealTimeIOxS() / conf.padding_layer(b'\x01\x02')
+p == Profisafe(load=b'ABC', Control_Status=0x20, CRC=0x123456, config={'length': 7, 'CRC': 3}) / PNIORealTimeIOxS() / conf.padding_layer(b'\x01\x02')
 
 = Profisafe with a CRC-32
-str(Profisafe(load='ABC', Control_Status=0x33, CRC=0x12345678, config={'length': 8, 'CRC': 4})) == b'ABC\x33\x12\x34\x56\x78'
+raw(Profisafe(load=b'ABC', Control_Status=0x33, CRC=0x12345678, config={'length': 8, 'CRC': 4})) == b'ABC\x33\x12\x34\x56\x78'
 
 = Profisafe is capable of dissected uncomplete packets
 p = Profisafe('AB', config={'length': 7, 'CRC': 3})
-p == Profisafe(load='AB', Control_Status=0, CRC=0)
+p == Profisafe(load=b'AB', Control_Status=0, CRC=0)
 
 
 + Check PNIORealTime layer
 
 = PNIORealTime default values
-str(PNIORealTime()) == b'\0' * 40 + b'\0\0\x35\0'
+raw(PNIORealTime()) == b'\0' * 40 + b'\0\0\x35\0'
 
 = PNIORealTime default values under an UDP packet
-str(UDP(sport=0x1234) / ProfinetIO(frameID=0x8002) / PNIORealTime()) == '12348892001a00008002'.decode('hex') + b'\0' * 12 + b'\0\0\x35\0'
+raw(UDP(sport=0x1234) / ProfinetIO(frameID=0x8002) / PNIORealTime()) == hex_bytes('12348892001a00008002') + b'\0' * 12 + b'\0\0\x35\0'
 
 = PNIORealTime simple packet
 * a simple data packet with a raw profinet data and its IOPS, an IOCS and a Profisafe data and its IOPS. 15B data length, 1B padding (20 - 15 -4)
-str(PNIORealTime(len=20, dataLen=15, cycleCounter=0x1234, dataStatus='redundancy+validData+no_problem', transferStatus=3,
+raw(PNIORealTime(len=20, dataLen=15, cycleCounter=0x1234, dataStatus='redundancy+validData+no_problem', transferStatus=3,
   data=[
       PNIORealTimeRawData(load=b'\x01\x02\x03\x04', config={'length': 5}) / PNIORealTimeIOxS(),
       PNIORealTimeIOxS(dataState='bad'),
       Profisafe(load=b'\x05\x06', Control_Status=0x20, CRC=0x12345678, config={'length': 7, 'CRC': 4}) / PNIORealTimeIOxS()
       ]
-  )) == '0102030400800005062012345678800012342603'.decode('hex')
+  )) == hex_bytes('0102030400800005062012345678800012342603')
 
 = PNIORealTime dissects to PNIORealTimeRawData when no config is available
-p = PNIORealTime('0102030400800005062012345678800012342603'.decode('hex'))
+p = PNIORealTime(hex_bytes('0102030400800005062012345678800012342603'))
 p == PNIORealTime(len=20, dataLen=15, cycleCounter=0x1234, dataStatus='redundancy+validData+no_problem', transferStatus=3, padding=b'\0',
   data=[
-      PNIORealTimeRawData(load='010203040080000506201234567880'.decode('hex'))
+      PNIORealTimeRawData(load=hex_bytes('010203040080000506201234567880'))
       ]
   )
 
@@ -94,7 +94,7 @@ pnio_update_config({
     (-8, Profisafe, {'length': 7, 'CRC': 4}),
     ]
   })
-p = Ether('000102030405060708090a0b889280020102030400800005062012345678800012342603'.decode('hex'))
+p = Ether(hex_bytes('000102030405060708090a0b889280020102030400800005062012345678800012342603'))
 p == Ether(dst='00:01:02:03:04:05', src='06:07:08:09:0a:0b') / ProfinetIO(frameID=0x8002) / PNIORealTime(
   len=20, dataLen=15, cycleCounter=0x1234, dataStatus='redundancy+validData+no_problem', transferStatus=3, padding=b'\0',
   data=[
@@ -110,8 +110,8 @@ p == Ether(dst='00:01:02:03:04:05', src='06:07:08:09:0a:0b') / ProfinetIO(frameI
 bind_layers(UDP, ProfinetIO, dport=0x8894)
 bind_layers(UDP, ProfinetIO, sport=0x8894)
 
-packets = [Ether('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'.decode("hex")),
-           Ether('0009914420170090274ee3fc0800450000c0b28800008011727a0a0a00960a0a0081061e889400ac689504000800100000000000a0de976cd111827100010003015a0100a0de976cd111827100a02442df7ddbabbaec1d005443b2500b01630abafd0000000001000000000000000500ffffffff54000000000040800000400000004080000000000000400000000009003c0100000a0000000000000000000000000000000000000000000000010000f84000008000000000000000000000000000000000000000000000000000'.decode("hex"))]
+packets = [Ether(hex_bytes('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')),
+           Ether(hex_bytes('0009914420170090274ee3fc0800450000c0b28800008011727a0a0a00960a0a0081061e889400ac689504000800100000000000a0de976cd111827100010003015a0100a0de976cd111827100a02442df7ddbabbaec1d005443b2500b01630abafd0000000001000000000000000500ffffffff54000000000040800000400000004080000000000000400000000009003c0100000a0000000000000000000000000000000000000000000000010000f84000008000000000000000000000000000000000000000000000000000'))]
            
 analysed_data = PNIORealTime.analyse_data(packets)
 assert len(analysed_data) == 2
diff --git a/scapy/fields.py b/scapy/fields.py
index 09534ade2..18d754fb6 100644
--- a/scapy/fields.py
+++ b/scapy/fields.py
@@ -665,7 +665,7 @@ class XStrFixedLenField(StrFixedLenField):
 
 class StrLenFieldUtf16(StrLenField):
     def h2i(self, pkt, x):
-        return x.encode('utf-16')[2:]
+        return plain_str(x).encode('utf-16')[2:]
     def i2h(self, pkt, x):
         return x.decode('utf-16')