From 48feef4ac8ce87c5bcc19b4df03d34f382a4f21d Mon Sep 17 00:00:00 2001
From: Michael Zapf <github@mizapf.de>
Date: Mon, 6 Apr 2020 13:50:53 +0200
Subject: [PATCH] Fixed state machine and made TC signal asynchronous.

---
 src/devices/machine/74161.cpp | 43 ++++++++++++++++++++++-------------
 src/devices/machine/74161.h   |  8 ++++++-
 2 files changed, 34 insertions(+), 17 deletions(-)

diff --git a/src/devices/machine/74161.cpp b/src/devices/machine/74161.cpp
index 015e4dba6bd..64e935152f5 100644
--- a/src/devices/machine/74161.cpp
+++ b/src/devices/machine/74161.cpp
@@ -28,8 +28,9 @@ ttl7416x_device::ttl7416x_device(const machine_config &mconfig, device_type type
 	, m_cep(0)
 	, m_pclock(0)
 	, m_p(0)
+	, m_cetpre(0)
+	, m_ceppre(0)
 	, m_out(0)
-	, m_tc(0)
 	, m_synchronous_reset(synchronous_reset)
 	, m_limit(limit)
 {
@@ -64,7 +65,6 @@ void ttl7416x_device::device_start()
 	save_item(NAME(m_pclock));
 	save_item(NAME(m_p));
 	save_item(NAME(m_out));
-	save_item(NAME(m_tc));
 
 	m_output_func.resolve_safe();
 	m_tc_func.resolve_safe();
@@ -79,15 +79,12 @@ void ttl7416x_device::init()
 {
 	m_clear = 0;
 	m_pe = 1;
-	m_cet = 0;
-	m_cep = 0;
+	m_cet = m_cetpre;
+	m_cep = m_ceppre;
 	m_pclock = 0;
 	m_p = 0;
 
 	m_out = 0;
-	m_tc = 0;
-
-	m_tc = 0;
 }
 
 void ttl7416x_device::tick()
@@ -99,7 +96,7 @@ void ttl7416x_device::tick()
 	}
 
 	uint8_t last_out = m_out;
-	uint8_t last_tc = m_tc;
+	uint8_t last_tc = tc_r();
 
 	if (m_pe)
 	{
@@ -118,20 +115,30 @@ void ttl7416x_device::tick()
 		m_output_func(m_out);
 	}
 
-	if (m_tc != last_tc)
+	if (tc_r() != last_tc)
 	{
-		m_tc_func(m_tc);
+		m_tc_func(tc_r());
 	}
 }
 
+/*
+    State machine:
+    limit 16: 0->1->2->...->e->f(tc)->0
+    limit 10: 0->1->2->...->9(tc)->0
+              10->11->4(no tc)
+              12->13->4(no tc)
+              14->15->0(no tc)
+*/
 void ttl7416x_device::increment()
 {
-	m_out = (m_out + 1) % (m_limit + 1);
+	m_out++;
 
-	if (m_out == m_limit)
-		m_tc = 1;
-	else
-		m_tc = 0;
+	if (m_limit == 10)
+	{
+		if (m_out == 12 || m_out == 14) m_out = 4;
+		if (m_out == 10) m_out = 0;
+	}
+	m_out &= 0x0f;
 }
 
 WRITE_LINE_MEMBER( ttl7416x_device::clear_w )
@@ -201,7 +208,11 @@ READ_LINE_MEMBER( ttl7416x_device::output_r )
 	return m_out;
 }
 
+/*
+    TC is an asynchronous signal, depending on the current states of CET, CEP,
+    and the counter value.
+*/
 READ_LINE_MEMBER( ttl7416x_device::tc_r )
 {
-	return m_tc;
+	return ((m_cet==1) && (m_cep==1) && (m_out==m_limit-1))? 1:0;
 }
diff --git a/src/devices/machine/74161.h b/src/devices/machine/74161.h
index abc702ba398..0145e08a9fb 100644
--- a/src/devices/machine/74161.h
+++ b/src/devices/machine/74161.h
@@ -82,6 +82,9 @@ public:
 	DECLARE_READ_LINE_MEMBER( output_r );
 	DECLARE_READ_LINE_MEMBER( tc_r );
 
+	void set_cet_pin_value(int value) { m_cetpre = value; }
+	void set_cep_pin_value(int value) { m_ceppre = value; }
+
 protected:
 	// construction/destruction
 	ttl7416x_device(const machine_config &mconfig, device_type type, const char *tag, device_t *owner, uint32_t clock, bool synchronous_reset, uint8_t limit);
@@ -111,9 +114,12 @@ private:
 	uint8_t m_pclock;   // pin 2
 	uint8_t m_p;        // pins 3-6 from LSB to MSB
 
+	// Preset inputs
+	uint8_t m_cetpre;
+	uint8_t m_ceppre;
+
 	// outputs
 	uint8_t m_out;      // pins 14-11 from LSB to MSB
-	uint8_t m_tc;       // pin 15
 
 	const bool      m_synchronous_reset;
 	const uint8_t   m_limit;