Editing MOS Technology 6522 (section)

==IRQ output==
The NMOS 6522 has an [[open drain]] IRQ output that may be used in [[wired-OR]] interrupt circuits.  The WDC W65C22S, in contrast, has a [[totem pole output#Digital circuits|totem pole]] IRQ output that must be isolated from a wired-OR circuit by a [[Schottky diode]], due to the fact that the totem pole output actively drives the IRQ pin high when the W65C22S is not interrupting. This specific issue is resolved on the WDC W65C22N which is fitted with an open-drain IRQ output.<ref>[http://www.westerndesigncenter.com/wdc/w65c22-chip.cfm W65C22 Versatile Interface Adapter (VIA)]</ref>