From c352d8ae8c7339026b956f60f2bf69cefc4324f8 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Sun, 13 Oct 2019 23:04:57 -0400
Subject: [PATCH] Adds a received_data_ register, that presently can never
 fill.

---
 Components/6850/6850.cpp | 9 +++++----
 Components/6850/6850.hpp | 6 ++++--
 2 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/Components/6850/6850.cpp b/Components/6850/6850.cpp
index d955a30cd..1001c01ac 100644
--- a/Components/6850/6850.cpp
+++ b/Components/6850/6850.cpp
@@ -29,7 +29,8 @@ uint8_t ACIA::read(int address) {
 	} else {
 		LOG("Read status");
 		return
-			((next_transmission_ == NoTransmission) ? 0x02 : 0x00) |
+			((received_data_ == NoValue) ? 0x00 : 0x01) |
+			((next_transmission_ == NoValue) ? 0x02 : 0x00) |
 			(data_carrier_detect.read() ? 0x04 : 0x00) |
 			(clear_to_send.read() ? 0x08 : 0x00) |
 			(interrupt_request_ ? 0x80 : 0x00)
@@ -98,7 +99,7 @@ void ACIA::run_for(HalfCycles length) {
 
 	if(write_data_time_remaining) {
 		if(transmit_advance >= write_data_time_remaining) {
-			if(next_transmission_ != NoTransmission) {
+			if(next_transmission_ != NoValue) {
 				transmit.flush_writing();
 				consider_transmission();
 				transmit.advance_writer(transmit_advance - write_data_time_remaining);
@@ -116,7 +117,7 @@ void ACIA::run_for(HalfCycles length) {
 }
 
 void ACIA::consider_transmission() {
-	if(next_transmission_ != NoTransmission && !transmit.write_data_time_remaining()) {
+	if(next_transmission_ != NoValue && !transmit.write_data_time_remaining()) {
 		// Establish start bit and [7 or 8] data bits.
 		if(data_bits_ == 7) next_transmission_ &= 0x7f;
 		int transmission = next_transmission_ << 1;
@@ -145,7 +146,7 @@ void ACIA::consider_transmission() {
 		transmit.write(divider_ * 2, total_bits, transmission);
 
 		// Mark the transmit register as empty again.
-		next_transmission_ = NoTransmission;
+		next_transmission_ = NoValue;
 	}
 }
 
diff --git a/Components/6850/6850.hpp b/Components/6850/6850.hpp
index 5111d5c89..0ef3da4ff 100644
--- a/Components/6850/6850.hpp
+++ b/Components/6850/6850.hpp
@@ -69,8 +69,10 @@ class ACIA: public ClockingHint::Source {
 		} parity_ = Parity::None;
 		int data_bits_ = 7, stop_bits_ = 2;
 
-		static const int NoTransmission = 0x100;
-		int next_transmission_ = NoTransmission;
+		static const int NoValue = 0x100;
+		int next_transmission_ = NoValue;
+		int received_data_ = NoValue;
+
 		void consider_transmission();
 
 		bool receive_interrupt_enabled_ = false;