Measurement Computing Digital488 - Manual (Page 73)

Section 5 Service Information
5.1
Service Information
5.1 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.
5.2 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