Echelon Neuron - Manual (Page 43)

BP Relative
In the BP-relative addressing mode, the instruction argument is a general-
purpose register (R0 to R15). The register name is prefixed by an exclamation
mark (!) to indicate a displacement relative to the base page.
Example:
pop !R0 ; ( )
push !R2 ; ([R2], ...)
The pop !R0 instruction pops the value of TOS into the R0 register (byte 8 of the
base page). The push !R2 instruction pushes the contents of the R2 register
(byte 10 of the base page) into TOS.
BP Indexed
In the BP-indexed addressing mode, the instruction operand is TOS. The BP-
indexed addressing mode uses the value in TOS as an offset into the base page,
providing access to all 256 base-page bytes. The register name (TOS) is prefixed
by an exclamation mark (!) to indicate a displacement relative to the base page.
Because this addressing mode uses TOS for its operand, instructions that use
this addressing mode use NEXT for their argument.
Example:
pop !tos ; ( )
push !tos ; ([TOS], ...)
The pop !tos instruction pops the value of NEXT from the stack and places it
into the location within the base page specified by the value of TOS. The push
!tos instruction pushes the contents of the location within the base page,
specified by the value of TOS, into NEXT on the stack. That is, it pushes the
TOS-th byte of the base page into NEXT.
Indirect
In the indirect addressing mode, the instruction operand is the value that is at
the top of the return stack.
Example:
push [rsp] ; (z, ...)
The push [rsp] instruction pushes the contents of the top of the return stack
(pointed to by RSP) into TOS on the data stack. RSP is not changed.
Another instruction that uses the indirect addressing mode is the dbrnz
instruction, which uses this addressing mode for the branch destination. Its
reference to [RSP] is implied.
Relative
In the relative addressing mode, the instruction takes a relative address for its
operand; a distance rather than an absolute address (some instructions that use
relative addressing take a second operand). The branch destination is computed
by adding the relative address (the distance from the current IP) to the
Neuron Assembly Language Reference 33