Int's and Str's
There are several ways to manipulate ST strings and I integers (or A ASCII) registers.
1) Use the COP command. If you want to build a string that's stored in N11:1 through N11:4 (eight characters, from an ASCII read instruction from a device connected to channel 0), then first MOV 8 into N11:0. Then when you do the instruction COP #N11:0 #ST12:0 1, the first element of the ST data block, the length, will be what you want (that is, 8 characters), and you will get what you want and nothing else. COP's without the pre-defined length get very strange, since the first ASCII character pair wind up in the .LEN.
2) You can manipulate each ASCII pair individually as if it were an integer. Just as the address ST12:0.LEN references the length. ST12:0.DATA[0] references the first TWO characters in the string. .DATA[1] are the third and fourth characters, etc. A MOV N11:1 ST12:0.DATA[0] would replace the first two characters in ST12:0 with the data in N11:0.