diff --git a/milkymist/framebuffer/dvi.py b/milkymist/framebuffer/dvi.py
index 7f4b2ac74..953ac2806 100644
--- a/milkymist/framebuffer/dvi.py
+++ b/milkymist/framebuffer/dvi.py
@@ -9,7 +9,7 @@ class Encoder(Module):
 		self.c = Signal(2)
 		self.de = Signal()
 
-		self.output = Signal(10)
+		self.out = Signal(10)
 
 		###
 
@@ -44,7 +44,7 @@ class Encoder(Module):
 		]
 
 		# stage 4 - final encoding
-		cnt = Signal((5, True))
+		cnt = Signal((6, True))
 
 		s_c = self.c
 		s_de = self.de
@@ -56,33 +56,91 @@ class Encoder(Module):
 
 		self.sync += If(s_de,
 				If((cnt == 0) | (n1q_m == n0q_m),
-					self.output[9].eq(~q_m_r[8]),
-					self.output[8].eq(q_m_r[8]),
+					self.out[9].eq(~q_m_r[8]),
+					self.out[8].eq(q_m_r[8]),
 					If(q_m_r[8],
-						self.output[:8].eq(q_m_r[:8]),
+						self.out[:8].eq(q_m_r[:8]),
 						cnt.eq(cnt + n1q_m - n0q_m)
 					).Else(
-						self.output[:8].eq(~q_m_r[:8]),
+						self.out[:8].eq(~q_m_r[:8]),
 						cnt.eq(cnt + n0q_m - n1q_m)
 					)
 				).Else(
-					If((~cnt[4] & (n1q_m > n0q_m)) | (cnt[4] & (n0q_m > n1q_m)),
-						self.output[9].eq(1),
-						self.output[8].eq(q_m_r[8]),
-						self.output[:8].eq(~q_m_r[:8]),
+					If((~cnt[5] & (n1q_m > n0q_m)) | (cnt[5] & (n0q_m > n1q_m)),
+						self.out[9].eq(1),
+						self.out[8].eq(q_m_r[8]),
+						self.out[:8].eq(~q_m_r[:8]),
 						cnt.eq(cnt + Cat(0, q_m_r[8]) + n0q_m - n1q_m)
 					).Else(
-						self.output[9].eq(0),
-						self.output[8].eq(q_m_r[8]),
-						self.output[:8].eq(q_m_r[:8]),
+						self.out[9].eq(0),
+						self.out[8].eq(q_m_r[8]),
+						self.out[:8].eq(q_m_r[:8]),
 						cnt.eq(cnt - Cat(0, ~q_m_r[8]) + n1q_m - n0q_m)
 					)
 				)
 			).Else(
-				self.output.eq(Array(control_tokens)[s_c]),
+				self.out.eq(Array(control_tokens)[s_c]),
 				cnt.eq(0)
 			)
 
+class _EncoderTB(Module):
+	def __init__(self, inputs):
+		self.outs = []
+		self._iter_inputs = iter(inputs)
+		self._end_cycle = None
+		self.submodules.dut = Encoder()
+		self.comb += self.dut.de.eq(1)
+
+	def do_simulation(self, s):
+		if self._end_cycle is None:
+			try:
+				nv = next(self._iter_inputs)
+			except StopIteration:
+				self._end_cycle = s.cycle_counter + 4
+			else:
+				s.wr(self.dut.d, nv)
+		if s.cycle_counter == self._end_cycle:
+			s.interrupt = True
+		if s.cycle_counter > 4:
+			self.outs.append(s.rd(self.dut.out))
+
+def _bit(i, n):
+	return (i >> n) & 1
+
+def _decode_tmds(b):
+	try:
+		c = control_tokens.index(b)
+		de = False
+	except ValueError:
+		c = 0
+		de = True
+	vsync = bool(c & 2)
+	hsync = bool(c & 1)
+
+	value = _bit(b, 0) ^ _bit(b, 9)
+	for i in range(1, 8):
+		value |= (_bit(b, i) ^ _bit(b, i-1) ^ (~_bit(b, 8) & 1)) << i
+
+	return de, hsync, vsync, value
+
 if __name__ == "__main__":
-	from migen.fhdl import verilog
-	print(verilog.convert(Encoder()))
+	from migen.sim.generic import Simulator
+	from random import Random
+	
+	rng = Random(788)
+	test_list = [rng.randrange(256) for i in range(500)]
+	tb = _EncoderTB(test_list)
+	Simulator(tb).run()
+
+	check = [_decode_tmds(out)[3] for out in tb.outs]
+	assert(check == test_list)
+	
+	nb0 = 0
+	nb1 = 0
+	for out in tb.outs:
+		for i in range(10):
+			if _bit(out, i):
+				nb1 += 1
+			else:
+				nb0 += 1
+	print("0/1: {}/{} ({:.2f})".format(nb0, nb1, nb0/nb1))