ZX Interface 1

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The ZX Interface 1 is a communications and storage interface for the ZX Spectrum released by Sinclair Research.

It provided an RS-232 serial interface, as well as storage using Microdrives and networking capabilities through the Sinclair Network, a proprietary interface of Sinclair's. The Sinclair Network would later be supported by MGT's DISCiPLE interface.

Port Bit
7 6 5 4 3 2 1 0
0xf7 Read TX Data Net Input
Write Net Output / RX Data
0xef Read Busy DTR Gap Sync Write Protect
Write Wait CTS Erase R/W Comms Clock Comms Data
0xe7 Read Microdrive data read
Write Microdrive data write
  • TX Data is the value received by the serial port.
  • Net Input is the value read from the Sinclair Network port.
  • Bit 0 of port 0x7f is output to the serial port if Comms Data is set, or to the network port if Comms Data is reset.
  • DTR signals that the remote station wishes to send data, CTS signals that the Spectrum wishes to send data
  • Wait is used for network synchronisation.
  • When Erase is reset the tape is erased and data is written, when set data is read.
  • R/W instructs the microdrive to read or write. When R/W is set the microdrive runs, when reset it stops
  • Comms Data is the value to be shifted into the microdrive select flip-flop chain.
  • Comms Clock shifts the microdrive select bit along the chain.
  • Write Protect is raised when a writeable cartridge is present in the selected microdrive.
  • Gap and Sync are used to locate the correct block of data on the microdrive.