Sinclair ZX Spectrum User Manual

Chapter 7
60
Overlapping ROM socket footprints
The outline labelled U5 can be fitted with a 28-way DIL IC socket to allow an onboard
ROM to be used. The outline labelled P4 can be fitted with a 2 x 15-way edge
connector socket to allow the use of ZX Interface 2 ROM cartridges.
The table below summarises the different ROM modes supported by the SPECTRA
interface:
ROM
cartridge
present
Onboard
ROM
enabled
Paging
mode
enabled
Operating mode
No
No
Yes / No
Spectrum ROM permanently paged in
No
Yes
No
Onboard ROM permanently paged in
Yes
No
No
ROM cartridge permanently paged in
No
Yes
Yes
Onboard ROM paged in on ZX Interface 1 address
Yes
No
Yes
ROM cartridge paged in on ZX Interface 1 address
Summary of supported ROM modes
When an onboard ROM is not present, configuration switch 2 should always be set to
the off position. A ROM cartridge or an onboard ROM should only ever be inserted or
removed while the Spectrum is powered off, otherwise a crash will occur and damage
may result to the hardware. With an external ROM connected and enabled, it is the
state of configuration switch 3 that determines whether the Spectrum’s BASIC ROM
will be overridden or supplemented.
Overriding the Spectrum’s ROM
The Spectrum’s ROM can be overridden by setting configuration switch 3 to the off
position. The SPECTRA interface will automatically detect and enable a ROM cartridge
if one is plugged in, but to use an onboard ROM requires manually enabling it by
setting configuration switch 2 to the on position. Either form of external ROM will
remain enabled even after the Spectrum is reset. If an onboard ROM is fitted but
configuration switch 2 set to the off position then the onboard ROM is disabled and
will lie dormant. If a device connected behind the SPECTRA interface requests access
to the ROM address space then an onboard ROM or a plugged in ROM cartridge will
always be disabled.

Sinclair ZX Spectrum Specifications

General

Brand	Sinclair
Model	ZX Spectrum
Category	Desktop
Language	English