CORIO2 products require the following cables to link to a computer:
For C2-4000, C2-5000 and C2-7000 products:
A standard 'null-modem' cable - with a 9-way socket at both ends.
For all other CORIO2 (C2 and 1T-C2) products:
A standard 'straight' cable - with a 9-way socket on one end and a 9-way plug on the other.
'Straight' means that the cable is a one-to-one pin connection (pin 1 to pin 1, pin 2 to pin 2, etc.).
'Null modem' refers to the fact that there is no modem connecting the PC and CORIO2 unit and hence the cable has to cross over the transmit (TX) and receive (RX) connections - something the modem normally does. This then means the PC's TX is connected to the CORIO2 unit's RX and vice versa.
The RS232 standard is quite strict in its definitions of wiring and socket gender, but it is also confusing enough to cause cable manufacturers to get the wiring and socket gender wrong sometimes - in particular with references to DTE, DCE, etc.
DTE is 'Data Terminal Equipment' (eg. a computer). DCE is 'Data Communication Equipment' (eg. a modem). Thus a computer is connected to a modem (DTE to DCE) with a simple socket to plug cable. The DTE (PC) device had a plug on it (ie. pins) and the DCE (modem) device had a socket - hence the cable just had to perform a one to one wiring connection. The modem communicated with another modem, crossing-over the TX and RX in the process and DCE to DTE cable (plug to socket) linked the second modem to the second PC.
Whenever 2 computers are linked together (ie. DTE to DTE), there's no modem in the middle to cross over the TX and RX signals - hence you need a special type of cable with sockets on both ends and the TX and RX signals crossed-over within it. Hence the term 'null modem'.