ZX Interface 1
Encyclopedia
Peripheral
A peripheral is a device attached to a host computer, but not part of it, and is more or less dependent on the host. It expands the host's capabilities, but does not form part of the core computer architecture....
from Sinclair Research
Sinclair Research Ltd
Sinclair Research Ltd is a British consumer electronics company founded by Sir Clive Sinclair in Cambridge. Originally incorporated in 1973 as Ablesdeal Ltd., it remained dormant until 1976, and did not adopt the name Sinclair Research until 1981....
for its ZX Spectrum
ZX Spectrum
The ZX Spectrum is an 8-bit personal home computer released in the United Kingdom in 1982 by Sinclair Research Ltd...
home computer
Home computer
Home computers were a class of microcomputers entering the market in 1977, and becoming increasingly common during the 1980s. They were marketed to consumers as affordable and accessible computers that, for the first time, were intended for the use of a single nontechnical user...
, the ZX Interface 1 was launched in 1983. Originally intended as a local area network
Local area network
A local area network is a computer network that interconnects computers in a limited area such as a home, school, computer laboratory, or office building...
interface for use in school classrooms, it was revised before launch to also act as the controller for up to eight ZX Microdrive
ZX Microdrive
The ZX Microdrive is a magnetic tape data storage system launched in July 1983 by Sinclair Research for their ZX Spectrum home computer. The Microdrive technology was later also used in the Sinclair QL and ICL One Per Desk personal computers.-Development:...
high-speed tape-loop cartridge drives. It also included a DE-9 RS-232
RS-232
In telecommunications, RS-232 is the traditional name for a series of standards for serial binary single-ended data and control signals connecting between a DTE and a DCE . It is commonly used in computer serial ports...
interface capable of operating at up to 19.2 kbit/s — a rare instance of Sinclair using an industry-standard connector. At hardware level it was mainly a voltage adapter, the serial protocol being implemented in software by bit-banging
Bit-banging
Bit banging is a technique for serial communications using software instead of dedicated hardware. Software directly sets and samples the state of pins on the microcontroller, and is responsible for all parameters of the signal: timing, levels, synchronization, etc...
. This led to problems when receiving data, but not when transmitting.
A wedge-shaped device fitting underneath the ZX Spectrum, ZX Interface 1 contained 8 kB of ROM
Read-only memory
Read-only memory is a class of storage medium used in computers and other electronic devices. Data stored in ROM cannot be modified, or can be modified only slowly or with difficulty, so it is mainly used to distribute firmware .In its strictest sense, ROM refers only...
comprising the control software for the Microdrives, RS-232 port and network interface. This extended the error handler in the Sinclair BASIC
Sinclair BASIC
Sinclair BASIC is a dialect of the BASIC programming language used in the 8-bit home computers from Sinclair Research and Timex Sinclair...
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.
The device offered two network ports, allowing up to 64 ZX Spectrums to be daisy-chained using network leads up to 3 m (10 ft) long. The network, called ZX Net, used a proprietary CSMA
Carrier Sense Multiple Access
Carrier Sense Multiple Access is a probabilistic Media Access Control protocol in which a node verifies the absence of other traffic before transmitting on a shared transmission medium, such as an electrical bus, or a band of the electromagnetic spectrum."Carrier Sense" describes the fact that a...
-like protocol. Data could be sent or received at 100 kbit/s either to or from a numbered workstation, or broadcast to all nodes, allowing one machine to act as a server.
Two further revisions of the device's firmware were made following launch. These aimed to improve ZX Microdrive
ZX Microdrive
The ZX Microdrive is a magnetic tape data storage system launched in July 1983 by Sinclair Research for their ZX Spectrum home computer. The Microdrive technology was later also used in the Sinclair QL and ICL One Per Desk personal computers.-Development:...
cartridge formatting and access time, printing functions via the RS-232
RS-232
In telecommunications, RS-232 is the traditional name for a series of standards for serial binary single-ended data and control signals connecting between a DTE and a DCE . It is commonly used in computer serial ports...
interface, and other bugs in the firmware held in device's internal 8K ROM
Read-only memory
Read-only memory is a class of storage medium used in computers and other electronic devices. Data stored in ROM cannot be modified, or can be modified only slowly or with difficulty, so it is mainly used to distribute firmware .In its strictest sense, ROM refers only...
. Machine code
Machine code
Machine code or machine language is a system of impartible instructions executed directly by a computer's central processing unit. Each instruction performs a very specific task, typically either an operation on a unit of data Machine code or machine language is a system of impartible instructions...
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 presence of revised entry points.
The same protocol, renamed QLAN, was later used on the Sinclair QL
Sinclair QL
The Sinclair QL , was a personal computer launched by Sinclair Research in 1984, as the successor to the Sinclair ZX Spectrum...
. 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 of later ZX Spectrum models such as the +2 and +3, due to differences in ROM and expansion connector, therefore wasn't possible to connect and use the Microdrive units.
See also
- The ZX Interface 2ZX Interface 2The ZX Interface 2 was a peripheral from Sinclair Research for its ZX Spectrum home computer released in September 1983. It had two joystick ports and a ROM cartridge slot, which offered instant loading times. The joystick ports were not compatible with the popular Kempston interface, and thus...
– An interface providing joystickJoystickA joystick is an input device consisting of a stick that pivots on a base and reports its angle or direction to the device it is controlling. Joysticks, also known as 'control columns', are the principal control in the cockpit of many civilian and military aircraft, either as a center stick or...
and ROMRead-only memoryRead-only memory is a class of storage medium used in computers and other electronic devices. Data stored in ROM cannot be modified, or can be modified only slowly or with difficulty, so it is mainly used to distribute firmware .In its strictest sense, ROM refers only...
cartridge ports