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[[Amstrad]] released two [[RS232]] interfaces, both using the same input/output addresses - thereby and, ultimately, therefore establishing the standard for serial interfaces - but with significantly different hardware.

Software was supplied on ROM, mostly comprising utility RSXs commands for hobbyists rather than a comms application per se- though there was limited terminal emulation for connecting to the then-popular [[Prestel]] service]. The original, UK version included commands for file transfer entitled |SUCK and |BLOW, which used a proprietary Amstrad format similar to [[XModem]]-1k but, annoyingly, subtly incompatible. These commands were reputedly renamed for the US edition to avoid causing offence. Because of the external power supply and the poor quality of the software, this model failed to establish itself as the "standard" serial interface in the way that (say) the [[DDI-1]] did for disc drives. This allowed other serial interfaces to flourish, such as those sold by [[Cirkit]] and [[KDS]].

Not much is know about The software was a ROM version of Pace's terminal utility, [[Commstar]]. This was a user-friendly program with standard [[XModem]] file transfer functions. However, one foolish design decision was the idea of using a 24x80 screen with a single-line status display - though presenting a good user interface, this forced the use of software rather than hardware scrolling, making the interface please add!unusable for terminal emulation at any speed above 2400 baud.

== Technicals specsLike the original interface, the Pace design used an 8250 [[UART]] chip, which was reliable up to 9600 baud and could sometimes function at faster speeds. The possibility has been discussed of replacing this with a pin-compatible 16550 and gaining even faster transfer speeds, but this is not believed to have been tested. ==

== Alternative software == The limitations of the Commstar software, and the desire to use more recently developed file transfer protocols (such as [[CategoryXModem]]-1k, [[YModem]] and [[ZModem]]) meant that many users chose to use their Amstrad serial interface with third-party software. This included:Peripherals * [[Ansiterm]] - a fast AMSDOS utility (also known as ANSI.ARC)* [[Charley's Comms ROM]] - sideways ROM capable of 4800 baud terminal emulation* [[ZMP]] - ZModem file transfer under CP/M A vast range of comms software was available for [[CP/M]], including [[bulletin board]] hosts, offline readers (notably [[CRR]]- CP/M Read and Reply), and many terminals.

Image:amstrad RS232C.jpg|The RS232C versionoriginal, flawed Amstrad serial interface