--- nono/vm/scc.cpp	2026/04/29 17:05:17	1.1.1.12
+++ nono/vm/scc.cpp	2026/04/29 17:05:24	1.1.1.13
@@ -14,6 +14,10 @@
 #include "keyboard.h"
 #include "mpu.h"
 
+// InsideOut p.135
+static const busdata read_wait  = busdata::Wait(41 * 40_nsec);
+static const busdata write_wait = busdata::Wait(49 * 40_nsec);
+
 // コンストラクタ
 SCCDevice::SCCDevice()
 	: inherited()
@@ -165,6 +169,8 @@ SCCDevice::ResetChannel(MPSCCChan& chan)
 	chan.wr15 = 0xf8;
 
 	// RR0 b0,1=%0、b2,6=%1
+	chan.rxlen = 0;
+	chan.txlen = 0;
 	chan.tx_underrun = true;
 
 	// RR1 b1,2=%1、b3-7=%0
@@ -184,12 +190,10 @@ SCCDevice::ResetChannel(MPSCCChan& chan)
 	ResetChannelCommon(chan);
 }
 
-uint64
+busdata
 SCCDevice::Read(uint32 offset)
 {
-	uint64 data;
-
-	mpu->AddCycle(41);	// InsideOut p.135
+	busdata data;
 
 	switch (offset) {
 	 case 0:	// $E98001
@@ -207,14 +211,14 @@ SCCDevice::Read(uint32 offset)
 	 default:
 		VMPANIC("corrupted offset=%d", offset);
 	}
+
+	data |= read_wait;
 	return data;
 }
 
-uint64
+busdata
 SCCDevice::Write(uint32 offset, uint32 data)
 {
-	mpu->AddCycle(49);	// InsideOut p.135
-
 	switch (offset) {
 	 case 0:	// $E98001
 		WriteCtrl(mpscc.chan[1], data);
@@ -231,10 +235,11 @@ SCCDevice::Write(uint32 offset, uint32 d
 	 default:
 		VMPANIC("corrupted offset=%d", offset);
 	}
-	return 0;
+
+	return write_wait;
 }
 
-uint64
+busdata
 SCCDevice::Peek(uint32 offset)
 {
 	uint64 data;
@@ -1016,7 +1021,7 @@ SCCDevice::SetXC(MPSCCChan& chan)
 }
 
 // 割り込みアクノリッジ
-int
+busdata
 SCCDevice::InterruptAcknowledge()
 {
 	return GetSR2B();