Serie - Interface Rsx Systems - Rs1 - Rs - 232cHardware Peripheriques
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Green with envy over BBC owners who can use a wide variety of modems and printers? Well, you'll soon be in the pink with the RSI, says David Janda.

Amstrad owners who have been holding their breath waiting for a serial interface for the CPC 464 can breathe again at last. RSX Systems, of Manchester, has stepped into the breach and produced an RS232 interface that comes complete with its own internal power supply and a cassette contai ni ng a terminal emulator and serial printer driver.


The hardware for the RSI is housed in a black box, measuring 65 by 150 by 175mm. The interface is controlled by a dedicated Z80A cpu and comes with its own internal PSU. Two rocker type switches are used for power and CTS control (more on that later), a red LED is also provided to indicate that the RS1 is powered up.

Unlike certain manufacturers I could name (Acorn), a decent length of power supply cable is provided — 4ft to be exact. A total of 18in of ribbon cable is used to connect the RS1 to the Amstrad, so the unit can be connected up without a tight squeeze.

A D-type 25 way RS232 connector (male) is housed in the rear of the unit. Seven lines are used in all, catering for practically anything that you might wish to connect to the unit. The pins used are indicated in Table 1.

Table 1


  • 2 Transmit data T x D
  • 3 Receive data Rxd
  • 4 Request to send RTS
  • 5 Clear to send CTS
  • 7 Signal earth
  • 8 Data carry detect/data set ready DCD/DSR
  • 20 Data terminal ready DTR
It would appear that some items you would like to use may not be able to control the RTS or DTR line. If this is the case, the CTS line can be switched in so that it is always active. In other words, in this mode, the RSI will always transmit a clear to send signal. It's rare that you will experience this, but it's comforting to know that you can get round the problem if it arose.

The Amprint program allows you to use a printer with RS232 port, instead of the Centronics type. To achieve this, the program installs an extension to the Locomotive Basic, allowing the extra commands to be used within programs or in direct mode (see Table 2).

Once the re-direction has been enabled, any print command, such as print #8; "Farewell my friends" Or LIST #8 will be Sent to  the RS1 rather than the Centronics port. Printer spooling (of a sort) can be achieved by selecting a buffer size.

Amterm converts the CPC 464 into a dumb terminal, making communications with another computer locally (DCE), or remotely (DTE) possible. At present, a limited number of features are available, but RSX Systems will be producing an updated version with file transfer, VT100 emulation and other features.

Written in machine code, Amterm is menu-driven and enables the user to change terminal characteristics and program the serial port. Baud rates between 50 and 19200 can be selected independently for the CPC 464 and the host system, as can word lengths.

A second menu enables terminal characteristics to be set up. Here, it's possible to control echo, switch to inverse video, and change the screen colour between green and amber.

A very handy option allows the line feed sequence to be controlled not only for the host, but the RX1 as well. Basically, when communicating with another micro, a CR is only sent; however Amterm enables a line-feed to be inserted/removed.

In use

Plug-in-and-go is not the order of the day here. No RS232 cable is supplied so it is left up to the user to buy or make up their own. If you wish to go DIY, then you could get away with only spending a few quid; made-upcables will costalot more.

Another item on the shopping list may be a null-modem. This is a connector that 'twists'the lines — quite crucial if you wish to use the same cable for connecting up to a local micro and a remote system via a modem.

Unfortunately, the documentation is not too clear for those who may wish to wire up their own cables and more thought could have gone into this area. Another niggle is that the connecting ribbon cable at the RSX end . had no polarizing bump, I and is easily inserted the I wrong way round.

The unassuming RSX's large i case is due to the through connection of the system expansion bus.

Table 2 — commands

  • RSBAUD Select baud rate
  • RSPRINT Enable re-direction to serial interface
  • CENPRINT Restore printed output to Centronics port
  • RSABORT Clear buffer
  • RSHALT Disable printing
  • RSG0 Enable printing
  • RSHELP Displays extra commands
Amterm proved to be very nice indeed. Mode 2 is used when on-line and any incoming control codes are intercepted. XON/XOFF is provided and control characters are intercepted and displayed in textual form. I would have liked to have made some comments about the Amprint, but the program was corrupted on both sides of the tape.


A price tag of £74.95 is slightly over the top, but the unit is well built and worked without any problems. Amterm was excellent and it will be interesting to see the updated version. Highly recommended.

Availability Mail order only.


MANUFACTURER: RSX Systems (3 Weston Grove, North-enden, Manchester M22 4NR)
★ YEAR: 1985
★ PRICE: £74.95


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L'Amstrad CPC est une machine 8 bits à base d'un Z80 à 4MHz. Le premier de la gamme fut le CPC 464 en 1984, équipé d'un lecteur de cassettes intégré il se plaçait en concurrent  du Commodore C64 beaucoup plus compliqué à utiliser et plus cher. Ce fut un réel succès et sorti cette même années le CPC 664 équipé d'un lecteur de disquettes trois pouces intégré. Sa vie fut de courte durée puisqu'en 1985 il fut remplacé par le CPC 6128 qui était plus compact, plus soigné et surtout qui avait 128Ko de RAM au lieu de 64Ko.