st2xxx: Misc. notes (nw)

src/devices/cpu/m6502/st2205u.cpp

@@ -24,6 +24,10 @@
     * 512K ROM (may be disabled)
     * 32K SRAM
 
+    One important difference between the ST2205U and almost every
+    other ST2XXX MCU is that PRR[0] and IRR[0] are *not* inverted
+    relative to A14.
+
 **********************************************************************/
 
 #include "emu.h"

src/devices/cpu/m6502/st2xxx.cpp

@@ -124,6 +124,7 @@ u8 st2xxx_device::pdata_r(offs_t offset)
 
 void st2xxx_device::pdata_w(offs_t offset, u8 data)
 {
+	// Set output state (CMOS or open drain) or activate/deactive pullups for input pins
 	if (data != m_pdata[offset])
 	{
 		m_pdata[offset] = data;