[[Image:Amstrad_Computer_User8512_006.jpg|thumb|400px|right|The Cirkit serial link was used for the Cirkit Prestel link]]
ReportedlyThe Prestel Link Interface is a serial interface from [[Cirkit]] and [[HoneySoft]], it did "flourish"the interface was bundled with a modem (or actually, but almost nothing else an acoustic coupler). The interface is knownmainly intended for being used with that modem. It can be also used as a general purpose RS232 interface, but there are several restrictions: The outputs are TTL levels (which won't work with devices that insist on proper RS232 voltages), only a few baudrates are supported, only RX, TX, RTS, DSR are implemented (no CTS,DTR).
* Some information fragments are here: [['''Note''' - Cirkit]].reportedly also made a "Twin-port" serial interface (which probably used other chipset)
== Technical ==
* The interface uses only two I/O ports are unknown...?* Chipset: uses Port FADFh - [[8251 USART chip|8251 UART]] (according to the advert)Data register* Note Port FBDFh - [[8251 USART chip|8251 UART]] Status/Control register For details on the I/O ports see [[8251 USART chip]]. For details on the interface see [[Media:Cirkit reportedly also made prestel link hardware.txt|hardware.txt]]. The baudrates are derived from a "Twin-port" serial interface 614KHz oscillator, divided by 32 (=19.2KHz), the TX rate can be optionally further divided by 16 (=1200Hz) (this is done by setting the DTR bit, which probably used other chipsetis misused to latch the baudrate selection, rather than to output a DTR signal), the RX rate doesn't have such an extra divider. Moreover, that rates can be divided by 1, 16, or 64 (inside of the [[8251 USART chip]]. The officially supported RX/TX rates are 1200/1200, 300/300, and 1200/75 baud. Further undocumented rates are 19200/19200, 19200/1200, and 300/18.75 baud (though they may be too slow/fast to be of practical use).
== Pictures ==
<gallery>
Image:NoPicture.gif|Circuit board, etc.
Image:Amstrad_Computer_User8512_006.jpg|Advert (ACU, December 1985)
Image:ACU8701062.jpg|Advert (ACU, January 1987)
</gallery>
== Manual ==
Documentation is found on the driver cassette (files HARDWARE.DOC and RSX.DOC, which can be viewed or printed with LIST.BAS). Below are the two DOC files converted to TXT format:
* [[Media:Cirkit prestel link hardware.txt]]
* [[Media:Cirkit prestel link rsx.txt]]
== Downloads ==
* None such[[Media:CirkitPrestelLinkTapes.ZIP|Cirkit Prestel Link Drivers & Documentation on cassette]] - contains the following files:** MENU.BAS - Prestel Link, Terminal, Send/Receive File tool (versions 1.?0a without advert, 1.0a with advert, 1.0b)** USER.BIN - RSX Commands 1 (interface) (versions 1.0, 1.2, 1.3)** PRES.BIN - RSX Commands 2 (prestel) (versions 1.0, 2.0)** LIST.BAS - Tool for viewing/printing the DOC files on Side B (LIST.BAS is not included on the v1.0b tape image)** HARDWARE.DOC - Description of the I/O Ports and cable** RSX.DOC - Description of the RSX commands (USER.BIN and PRES.BIN) * [[Media:Cirkit Prestel Link 2.zip]] - version 2 - contains only one file:** CPL2 - some kind of terminal software or so
== Specs (from advert) ==
* Extensive documentation about interface and RSX's supplied on cassette.
[[Category:HardwareNetwork]] [[Category:Peripherals]] [[Category:Serial_interfaces]] [[Category:Communication Software]]