In Bascom gibt es sogar ein Befehl dafür:

Action:
Compact two bytes into a word or integer.

Syntax:
varn = MAKEINT(LSB , MSB)

Remarks:
Varn Variable that will be assigned with the converted value.
LSB Variable or constant with the LS Byte.
MSB Variable or constant with the MS Byte.

The equivalent code is:
varn = (256 * MSB) + LSB

Example:
Dim a As Integer, I As Integer
A = 2
I = Makeint(a , 1) 'I = (1 * 256) + 2 = 258
End