Cirkit hardware seems to be quite rare; at least there's little information about it in the internet.
Products
- Cirkit Prestel Link Amstrad Interface ("It looks like a cartridge (8x5cm) for an Amstrad with a passthrough edge connector and a lead (70cm) comming out with a 5-pin DIN plug (male) at the end.")
- Cirkit twin-port serial interface (resold by Microstyle)
- Cirkit serial interface
Not sure if above list is complete, or if some items are duplicated.
Notes
According to this webpage, [1], the Cirkit serial interface uses the same Port addresses as the Amstrad / Pace interfaces (most information on that webpage, especially the clock frequencies, baudrate, and chipset, seems to be incorrect, so not too sure if the part about Cirkit I/O ports is correct).