BigBo,

It depends on the control software. Some take input in hex, some in ASCII, some either. Usually they allow 'escape' characters, so that formats can be mixed. E.g. "cir 3339<CR><LF>" would represent your string above.

Note that you're being inconsistent with character case: your text examples always have a capital 'C' and lower case 'ir', but your hex strings are all lower case: "cir". I wouldn't presume equipment like that would do case translation; they are more likely to accept input very literally, and if the manual has "CIR", I'd use "CIR" in my string, or "Cir" if the manual says "Cir", etc. Upper case ASCII starts with "A" at hex 41, and lower case at hex 61.

Another very important aspect to serial control is baud rate and data format.  The most common data format is 8 data bits, 1 stop bit, no parity.  Many devices use 9,600 baud (speed), but some use much higher rates.  It's essential to match those specifications between the 'host' (control processor) and 'client' (controlled device).

Hope that helps.