difference btw splnet & splimp

[Dongman Lee]

What is the difference between "splnet" and "splimp"?   
I had a look at machine instructions of them in /sys/machine/asm.sed, but
I could not understand their roles completely becuase there is no description
for register 0x16 in /sys/machine/mtpr.h. 
What is the function of Reg.0x16?
For the record, I am using VAX750/4.2BSD.
Please mail me.
Thanx in advance.

T. A. D. Lee

Arpa: dmlee%cheviot%newcastle.mailnet at mit-multics.arpa
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