diff --git a/src/mame/drivers/macprtb.cpp b/src/mame/drivers/macprtb.cpp
index 84b5361a3fb..8950f7aa8c1 100644
--- a/src/mame/drivers/macprtb.cpp
+++ b/src/mame/drivers/macprtb.cpp
@@ -18,8 +18,8 @@
 
     These are sort of an intermediate step between the SE and Mac II in terms
     of functional layout: ASC and SWIM are present, but there's only 1 VIA
-    and an M50753 microcontroller "PMU" handles power management, ADB, and
-    clock/PRAM.
+    (CMDμ G65SC22PE-2, not the "6523" variant normally used in ADB Macs) and an
+    M50753 microcontroller "PMU" handles power management, ADB, and clock/PRAM.
 
     VIA connections:
     Port A: 8-bit bidirectional data bus to the PMU
@@ -282,6 +282,7 @@ void macportable_state::machine_start()
 	m_irq_count = m_ca1_data = m_ca2_data = 0;
 	m_pmu_via_bus = 0;
 	m_pmu_ack = m_pmu_req = 0;
+	m_adb_line = 1;
 
 	m_6015_timer = machine().scheduler().timer_alloc(timer_expired_delegate(FUNC(macportable_state::mac_6015_tick),this));
 	m_6015_timer->adjust(attotime::never);
@@ -550,7 +551,7 @@ void macportable_state::macprtb(machine_config &config)
 	SCC85C30(config, m_scc, C7M);
 //  m_scc->intrq_callback().set(FUNC(macportable_state::set_scc_interrupt));
 
-	R65NC22(config, m_via1, C7M/10);
+	R65C22(config, m_via1, C7M/10);
 	m_via1->readpa_handler().set(FUNC(macportable_state::mac_via_in_a));
 	m_via1->readpb_handler().set(FUNC(macportable_state::mac_via_in_b));
 	m_via1->writepa_handler().set(FUNC(macportable_state::mac_via_out_a));