Echelon Neuron - Manual (Page 97)

DROP_R (Drop from Stack and Return)
The DROP_R instructions drop a value from the data stack and perform a
return from call operation:
• The DROP_R TOS instruction drops TOS and performs a return from
call
• The DROP_R NEXT instruction drops NEXT and performs a return
from call
The DROP_R instruction uses the direct addressing mode.
Note that the DROP_R TOS instruction is equivalent to the DEALLOC #1
instruction.
The DROP_R instruction applies to Series 3100, 5000, and 6000 devices.
Syntax:
The DROP instruction requires a single operand to specify which stack element
to drop:
DROP_R TOS
DROP_R NEXT
Table 31 describes the attributes of the DROP_R instruction.
Table 31. DROP_R Instruction
Instruction Hexadecimal
Opcode
Instruction
Size (Bytes)
CPU Cycles
Required
Affect on
Carry Flag
DROP_R TOS 7F 1 6 None
DROP_R NEXT F5 1 5 None
Example:
The following example implements a function named set_mode, which uses
conditional compilation to perform different tasks for different modes. If the
mode MODE1 is defined, the function consumes the TOS value by using the POP
instruction. If the mode MODE1 is not defined, the function uses the DROP_R
TOS instruction to drop the mode argument from the data stack and return to
the function’s caller.
set_mode ; (mode)
IFDEF MODE1
; Limit to 0 or 1
and #h'1
pop _mode ; ()
ret ; return to caller
ELSE
drop_r tos ; ()
ENDIF
Neuron Assembly Language Reference 87