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9.25.3 PDP-11 Assembly Language Syntax

as supports both DEC syntax and BSD syntax. The only difference is that in DEC syntax, a # character is used to denote an immediate constants, while in BSD syntax the character for this purpose is $.

general-purpose registers are named r0 through r7. Mnemonic alternatives for r6 and r7 are sp and pc, respectively.

Floating-point registers are named ac0 through ac3, or alternatively fr0 through fr3.

Comments are started with a # or a / character, and extend to the end of the line. (FIXME: clash with immediates?)