Chapter 1
8
The large square integrated circuit (IC) situated at the centre of the board implements
the core logic that controls the facilities of the SPECTRA interface. It is a high capacity
complex programmable logic device (CPLD) and is analogous to the uncommitted
logic array (ULA) inside the Spectrum.
The interface includes a set of switches that allow specific features to be individually
enabled or disabled, thereby achieving maximum compatibility with other interfaces
and existing software. By default, the SPECTRA board is shipped with all switches set
to the disabled position and hence it initially functions only as a SCART interface.
The video signal absent indicator provides visual feedback should the SPECTRA
interface detect a problem with the signals used from the Spectrum expansion bus
that prevent it from displaying a TV picture via the SCART socket. The indicator, a light
emitting diode (LED), will shine red if such an error is detected. The condition under
which this can occur is described in Chapter 3.
The following items are not included by default with the SPECTRA interface and so
must be obtained separately if the corresponding feature is to be used:
A SCART cable which supports an RGB connection. The vast majority of
commercially available SCART cables will be suitable. The wiring of the cable
required is described in Chapter 3.
A 2 x 15-way edge connector socket (if ROM cartridge support is required).
A 28-way dual-in-line (DIL) IC socket (if an onboard ROM is required).
A serial cable for use with the RS232 socket. The wiring of the cable required is
described in Chapter 6.
In addition, the television must have an RGB enabled SCART socket. There are three
different video formats that a SCART socket may support (RGB, composite video and
S-video) but often a socket will not support all of these. Televisions which have more
than one SCART socket may implement support for a different subset of video formats
on each socket, and so all available sockets should be tried until one is found which
yields a picture. It is advisable to consult the television instruction manual to determine
which of its SCART sockets provide support for connection via RGB.
Throughout the rest of this manual the terms expansion port and expansion bus are
used interchangeably to refer to the connection socket located at the rear of the
Spectrum and on some peripherals. Likewise, the terms interface, peripheral and
device are used interchangeably and refer to a physical board that can be plugged
into the Spectrum’s expansion port.
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