Ok, having now spent 10 minutes glancing through the Holy Grail that is The programmer's Reference Guide I am now an expert

...well not really as nothing happened.
Using the "Edit Button Script" command in Mach3's Operator tab menu I highlighted the REF ALL HOME button and added the following code:
SendSerial("B0000133E167R25") in a feeble attempt to send B0000133E167R25 to the serial port. Of course, nothing happened when I cycled through the code.
I have changed the baud rate in General Logic Configurations and ticked Event Friven Serial Control in Engine Configuration, though I am unsure what that does.
REF ALL HOME script now looks like this:
DoButton( 24 )
DoButton( 23 )
DoButton( 22 )
DoButton( 25 )
SendSerial("B0000133E167R25")
DoOEMButton(133)
DoOEMButton(134)
DoOEMButton(135)
So what am I doing wrong?
...Sweep