Schneider RS232 Interface

From CPCWiki - THE Amstrad CPC encyclopedia!
Jump to: navigation, search

RS232 Interface for the CPC by Schneider. Schneider is the German distributor for Amstrad CPC hardware (however, this interface was Schneider's own invention, not an Amstrad product).


The original Schneider RS232 Interface was released around 1985. Two years later, in 1987, a software-compatible clone was released as DIY schematic in a German book (link). Even later, around 1996, a copy of that DIY schematic also circulated in the internet (link). The DIY port address, timings and handshake signals are exactly the same as in the original Schneider version - except that DCD (Data Carrier Detect) isn't implemented in the DIY version.


I/O Ports

Default I/O addresses are F8E0h-F8EFh (though the interface can be jumpered to use different addresses).

F8E0h - Z80-STI Indirect Data Register
F8E1h - Z80-STI General Purpose I/O Data Register
F8E2h - Z80-STI Interrupt Pending Register B      ;\
F8E3h - Z80-STI Interrupt Pending Register A      ;
F8E4h - Z80-STI Interrupt in-Service Register B   ; not used
F8E5h - Z80-STI Interrupt in-Service Register A   ;
F8E6h - Z80-STI Interrupt Mask Register B         ;
F8E7h - Z80-STI Interrupt Mask Register A         ;/
F8E8h - Z80-STI Indirect Index and Interrupt Vector Register
F8E9h - Z80-STI Timers A and B Control Register   ;\
F8EAh - Z80-STI Timer B Data Register             ; not used
F8EBh - Z80-STI Timer A Data Register             ;/
F8ECh - Z80-STI USART Control Register
F8EDh - Z80-STI Receiver Status Register
F8EEh - Z80-STI Transmitter Status Register
F8EFh - Z80-STI USART Data Register

Aside from the above 16 directly addressable registers, there are 8 indirectly addressable ones. For details on the direct & indirect registers, see Z80-STI.


  • Supported by "Starwriter".
  • BASIC example (for the official version) is found in the Schneider RS232 manual (see below scans)
  • ASM example (for the DIY version) is included with Tim Riemann's RS232 interface

Manual (German)


The uncommon shape of the housing dates back to a Schneider BTX modul (which was being intended to be plugged into Schneider Television Sets). Apparently Schneider produced too many housings, and re-used them for the RS232 interface. Actually, a RS232 interface is very much the same as a BTX interface (the actual BTX modem must be rented separately from Deutsche Bundespost), so even the PCB may be (almost/exactly?) the same for both devices.


A review appeared in German magazine CPC Schneider International (issue 12-1985, pages 38, 39).


  • A "Z80 STI" is a 40pin MK3801 chip from Mostek. Details on that chip are from the "MOSTEK 1982/1983 Microelectronic Data Book" (kindly made available by John Robertson).