Editing ZX Interface 1 (section)

{{Short description|Peripheral for the ZX Spectrum}}
{{more citations needed|date=February 2019}}
{{Use British English|date=December 2019}}
{{Use dmy dates|date=December 2019}}
[[Image:ZX Interface1 Microdrive.jpg|thumb|The ZX Interface 1 with the ZX&nbsp;Microdrive connected]]

The '''ZX Interface 1''', launched in 1983, was a [[peripheral]] from [[Sinclair Research Ltd|Sinclair Research]] for its [[ZX Spectrum]] [[home computer]]. Originally intended as a [[local area network]] interface for use in school classrooms, it was revised before launch to also act as the controller for up to eight [[ZX Microdrive]] high-speed tape-loop cartridge drives. It also included a [[DE-9]] [[RS-232]] interface capable of operating at up to 19.2&nbsp;kbit/s. At hardware level it was fundamentally a voltage adaptor, the serial protocol being implemented in software by [[bit-banging]]. This led to problems when receiving data, but not when transmitting.

A wedge-shaped device fitting underneath the ZX Spectrum, the Interface 1 required two screws to be removed from the underside of the Spectrum, the existing screwholes being used by longer screws running through the ZX Interface 1 to stop it from inadvertently becoming detached. The Interface 1 contained {{nowrap|8 kB}} of [[Read-only memory|ROM]] comprising the control software for the Microdrives, an RS-232 port and network interface. This extended the error handler in the [[Sinclair BASIC]] to allow extra keywords to be used. As this became an official standard, other developers quickly used this mechanism to create language extensions to Sinclair BASIC.

Two further revisions of the device's firmware were made following launch.<ref name="YS10.26">[http://www.users.globalnet.co.uk/~jg27paw4/yr10/yr10_26.htm Interface 1], Issue 10, December 1984, Your Spectrum 10</ref> These aimed to improve [[ZX Microdrive]] cartridge formatting and access time, printing functions via the [[RS-232]] interface, and other bugs in the firmware held in the device's internal 8K [[Read-only memory|ROM]]. [[Machine code]] software which used the officially documented entry points ('hook codes') would experience few incompatibility issues; however, programs using non-standard entry points risked incompatibility due to the presence of revised entry points.

The same protocol, renamed '''QLAN''', was later used on the [[Sinclair QL]]. This was intended to be interoperable with ZX Net, but due to timing differences interoperability was found to be problematic.

The ZX Interface 1 was incompatible with some later ZX Spectrum models such as the +2A and +3, due to differences in ROM and in the expansion connector. It was therefore impossible to connect and use the Microdrive units with these later models. It did, however, work with the original +2, although the much larger case made the interface an awkward fit.