ZX Net

Interface 1 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-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.

ZX Net concept

 * network use 1 bidirectional data wire
 * all ZX Spectrum has a network station number (range 1 to 64)
 * station number 0 used to indicate broadcast
 * data broke up max. 255 byte length packets
 * every packet has a 8 byte length packet header
 * every packet has a serial number
 * the packet and the header have checksum
 * last packet in the chain is marked, so the receiving end is know about end of data
 * the receiving end send a response byte (value 0x01) after got the good excepted header or packet except broadcast
 * if sender does not got the respons byte in time, send the header or packet again