Digital488 User’s Manual 916895 Service Information, 5-1
Service Information 5
Factory Service
IOtech maintains a factory service center in Cleveland, Ohio. If problems are encountered in using the
Digital488 you should first telephone the factory. Many problems can be resolved by discussing the
problems with our applications department. If the problem cannot be solved by this method, you will be
instructed as to the proper return procedure.
Theory of Operation
The Heart of the Digital488 is a 6809 microprocessor [U101] supported by 8K bytes of firmware EPROM
[U102 (2764)] and 8K bytes of static RAM [U103 (6264)]. 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 digital I/O ports are controlled by 'PIA's [U202-U204 (68B21)]. SW1 is read through one port
of U204.
Power is supplied by an external unregulated 9 volt wall mount supply. Regulation to the required +5 volts
is provided by U109 [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
$6000-$7FFF U103 6264 Static RAM
$9200-$9204 U202 6821 Digital I/O
$9400-$9404 U203 6821 Digital I/O
$9800-$9804 U204 6821 Digital I/O
$A000-$A007 U106 TMS9914A IEEE Controller
$B000-$B00F U104 R65C22 VIA
$E000-$FFFF U102 2764 Programmed EPROM
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