Specifications
Acorn Enhanced Expansion Card Issue 5, August 1994 23
Acorn Enhanced Expansion Card
shown on Acorn drawing Number 0297,093. The
gasket is fitted on the inside of the back panel. To
guarantee correct EMC performance the Risc PC
should always contain a blanking gasket in each
unused expansion card slot.
• All external connectors should be of a robust,
recognised EMC design.
• All external connectors should have a comprehensive
low impedance bond to the rear panel.
• The rear panel must be conductive and fitted to the
host computer frame via low impedance fixings.
• Any painted finish on the rear panel must not cause
the expansion card to be isolated from the computer's
earthing system.
• When fitted, there should not be any continuous slot
longer than 20mm around the expansion card rear
panel.
• Any external cables must have an EMC performance
that does not compromise the host computer system.
• If external cables are required for the card, but not
supplied, full details of the recommended cable,
connectors and construction methods of the leads
should be specified.
• A four-layer PCB is preferred together with a good
layout.
• Connection of the card 0V line and the rear panel is
not generally recommended. However, on some PCB
designs this may be found to give an improvement in
static immunity.
• Be aware that the rear panel may be subject to high
current earth continuity testing; see the Safety testing:
Electricity at work regulations, 1989 on page 22.
• The EMC performance of the card must not
deteriorate as a result of insertion and removal during
the life of the product.
Mechanical specification
Expansion cards should be built to the specifications
given in drawing number 0276,099, noting that the
thickness of the back panel is 1.6mm. This drawing and
drawing number 0276,204 give the relevant dimensions
of single- and double-width expansion cards, and their
mounting brackets respectively. Both drawings are
attached. Note that not all machines support both single-
and double-width cards.
Mini expansion cards are described in drawing number
0280,080, attached.
Note that solder tails should be no longer than 2mm.
Blanking panels
Single-width expansion cards not targeted at the
Risc PC should be accompanied by a single-width
blanking panel and T-piece, to blank off the aperture
otherwise left when the full-width Acorn blanking panel is
removed to fit the card. Drawings of the T-piece
(0276,036) and the blanking panel (0276,035) are
attached.
To minimise costs to Risc PC owners, it may be
advisable to provide a blanking panel and T-piece as a
separate installation kit.
Paint specification
The cream paint colour for back panels on machines
prior to the Risc PC is RAL 1013C. For the Risc PC, the
paint colour is PMS Cool Grey 2. Expansion cards which
are designed to fit machines of all types can be finished
in nickel plate, and need not be painted.
Archimedes 300 series and 440
computers and R140 workstations
Note that the expansion card slot in Archimedes 300
series, 440 and some R140 machines is 2.5mm shorter
than it should be (from backplane to rear panel) for a
standard Eurocard. This was corrected for Archimedes
400/1 series, R260 and later computers. Expansion
cards which may be used by these earlier computers
should therefore be supplied with two spacers (see the
attached drawing, number 0276,227, for details of the
spacer). This will allow the expansion card to be seated
securely, without causing the backplane to lean
excessively towards the front of the machine.
The original screws supplied with the computer will be
long enough to accommodate the spacers, provided that
the expansion card backplate thickness does not exceed
1.6mm. If your card has a thicker rear panel, you may
need to supply longer fixing screws.
Fitting
The diagram below shows how the spacers are fitted to
earlier computers:
Figure 22: Fitting spacers to earlier models
Marking
Each card should, whenever possible, be marked on the
external face of the panel with the manufacturer’s ID and
the expansion card ID.
SPACER
REAR PANEL OF
EXPANSION CARD
WASHER
SCREW