Black Box IC026A-R2, IC026AE-R2 manual Theory of Operation, Address Device Part Number Function

RS-232↔IEEE 488 INTERFACE CONVERTER

7.Theory of Operation and Board Layout

7.1Theory of Operation

The heart of the interface converter is a 6809 microprocessor (U101) supported by 8K bytes of firmware EPROM [U102 (2764)] and 32K bytes of static RAM [U103 (58256)]. A Versatile Interface Adapter [U104 (65B22)] is used to generate real-time interrupts for the firmware operating system.

The front-panel annunciators are also driven by U104 through an inverter [U113 (74LS04)]. The IEEE 488 bus interface is accomplished by a TMS9914A [U106] controller with drivers U107 and U108. The serial interface is provided by the UART [6551 (U105)]. If RS-232 levels are chosen, they are provided by the RS-232 transceiver (U209). If RS-422 levels are selected, the differential driver [26LS30 (U207)] and receiver [26LS33 (U208)] are used.

The internal DIP switches [SW1, SW2, and SW3] are read via 74HCT244 tri-state buffers [U201, U202 and U203]. Power is supplied by an external unregulated 9-volt wallmount supply. Regulation to the required +5 volts is provided by U206 [7805].

Decoding of the microprocessor address space is accomplished with a Programmable Logic Array [U110 (16L8)]. The Memory space allocation is:

Address	Device	Part Number	Function
$0000-$7FFF	U103	58258	Static RAM
$A000-$A007	U106	9914A	IEEE Controller
$A800-$A807	U105	6551	UART
$B000-$B00F	U104	65B22	VIA
$B800	U201	74HCT244	SW1 (S201)
$B801	U202	74HCT244	SW2 (S202)
$B802	U203	74HCT244	SW3 (S203)
$E000-$FFFF	U102	2764	Programmed EPROM

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