ZXI standard: Difference between revisions

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[[File:zxi.png|128px|thumb|ZXI logo]]
[[File:zxi.png|thumb|ZXI logo]]
[[File:zxi_outline.png|128px|thumb|ZXI outline logo]]
[[File:zxi_outline.png|64px|thumb|ZXI outline logo]]
The ZXI (ZX Interface) standard is for devices that are attached to the Spectrum edge connector. ZXI compliant devices are inter-operable with each other without conflicts. Certified devices may display the logo on their case, in their manuals, and on-screen.
The ZXI (ZX Interface) standard is for devices that are attached to the Spectrum edge connector. ZXI compliant devices are inter-operable with each other without conflicts. Certified devices may display the logo on their case, in their manuals, and on-screen.


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The Z80 provides 16-bit I/O decoding, so in theory the Spectrum has 65536 ports available for hardware devices. In practice the Spectrum does not fully decode the I/O and there are no spare I/O ports available that do not clash with at least one existing peripheral. For example, the ULA alone uses 32768 ports (every even port). It is worth noting that the Timex clones do fully decode the I/O ports.
The Z80 provides 16-bit I/O decoding, so in theory the Spectrum has 65536 ports available for hardware devices. In practice the Spectrum does not fully decode the I/O and there are no spare I/O ports available that do not clash with at least one existing peripheral. For example, the ULA alone uses 32768 ports (every even port). It is worth noting that the Timex clones do fully decode the I/O ports.


During the development of the ULAplus replacement ULA, a comprehensive search was carried out to determine a 16-bit port range that clashed with the least devices. An 8-bit port was located that clashed with a single device, the ZX Printer, and a hardware fix created to prevent the ZX Printer using that address.
During the development of the [[ULAplus]] replacement ULA, a comprehensive search was carried out to determine a 16-bit port range that clashed with the least devices. An 8-bit port was located that clashed with a single device, the ZX Printer, and a hardware fix created to prevent the ZX Printer using that address.
The following modification to the ZX Printer circuit prevents it being triggered by access to port xx3B.
The following modification to the ZX Printer circuit prevents it being triggered by access to port xx3B.


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'''Port allocations are currently in flux - be advised that assignments may change in the future'''
'''Port allocations are currently in flux - be advised that assignments may change in the future'''


To have your device certified as ZXI compliant, you must apply for the required number of I/O ports in the range #hh3B. This can be done by posting a request to usenet's comp.sys.sinclair, or to the [http://alistairsserver.no-ip.org/mailman/listinfo/zxi-specification-discussion zxi-specification-discussion mailing list]
To have your device certified as ZXI compliant, you must apply for the required number of I/O ports in the range #hh3B. This can be done by sending a message via https://www.facebook.com/cheverongroup/.


'''Allocations as of 05 September 2012'''
'''Allocations as of 05 September 2012'''
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#FF  : ULAplus data
#FF  : ULAplus data
#FE  : ZX Prism Palette Control
#FE  : ZX Prism Palette Control
#EF-FD: Unassigned
#FD  : ZX-UNO
#FC  : ZX-UNO
#FB  : ZXID system
#EF-FB: Unassigned
#EE  : ZX Prism (?)
#EE  : ZX Prism (?)
#E0-ED: Unassigned
#E0-ED: Unassigned
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