MEMORY PLUS Manual By Lee Davison and Hans Otten Back to The Computerist

				VERSATILE INTERFACE ADAPTER

	The 6522 Versatile Interface Adapter is one of the important pluses of
	MEMORY PLUS.  This sophisticated chip has the following basic features:


	  I/O:	Two 8-bit parallel I/O ports with additional handshaking
		control lines.  This more than doubles the basic KIM-i
		I/O capabilities.

	  TIMERS:  Two powerful interval timers which have a number of
		operating modes permitting them to be used as counters1
		"free-running" timers, "one-shot" timers, and more.

	  SHIFT REGISTER:  Perform serial I/O under control of a timer, the
		system clock or an  external signal.  Serial-to-parallel and
		parallel-to-serial conversions take place within the 6522
		without involving the MICRO on a bit-by-bit basis.

	  INTERRUPTS:  The many different devices on the 6522 can cause
		interrupts to signal the completion of activity. These
		interrupts can be individually enabled, disabled and
		tested.

	The 6255 chip has two functions on MEMORY PLUS.  The first is to provide all
	of the 6522 capabilities to the user as an extension of the MICRO.  The
	second is to control the EPROM Programmer.  The 6522 is the heart of the EPROM
	Programmer.  When the system is being used to program EPROMs, then the 6522,
	as well as several I/O lines from the basic MICRO, is dedicated to this task.
	See the section on "EPROM Programming" for details.

	The addressing of the 6522 is determined by a +5 signal generated by the MEMORY
	PLUS board and the AB8 and AB9 address signals.  The sixteen internal registers
	of the 6522 normally have the following addresses and functions:

		6200	ORB  Output Register B/Input Register B
		6201	ORA  Output Register A/Input Register A With Handshake
		6202	DDRB   Data Direction Register B
		6203	DORA   Data Direction Register A
		6204	T1C-L       Timer/Counter 1 Low
		6205	T1C-H       Timer/Counter 1 High
		6206	T1L-L       Timer/Counter 1 Low
		6207	T1L-H       Timer/Counter 1 High
		6208	T2C-L       Timer/Counter 2 Low
		6209	T2C-H       Timer/Counter 2 High
		620A	SR          Shift Register
		620B	ACR         Auxiliary Control Register
		620C	PCR         Peripheral Control Register
		620D	IFR         Interrupt Flag Register
		620E	IER         Interrupt Enable Register
		620F	ORA2        Output Register A/Input Register A Without Handshake