Echelon Neuron - Manual (Page 96)

DROP (Drop from Stack)
The DROP instruction drops a value from one of the stacks:
• The DROP [RSP] instruction drops the top of the return stack
• The DROP TOS instruction drops TOS
• The DROP NEXT instruction drops NEXT
The DROP instruction uses the direct addressing mode.
The DROP 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 [RSP]
DROP TOS
DROP NEXT
Table 30 describes the attributes of the DROP instruction.
Table 30. DROP Instruction
Instruction Hexadecimal
Opcode
Instruction
Size (Bytes)
CPU Cycles
Required
Affect on
Carry Flag
DROP [RSP] F6 1 2 None
DROP TOS E4 1 3 None
DROP NEXT E5 1 2 None
Example:
The following example calls a function named clearFlags, which requires three
stack arguments. The function consumes one of the arguments, but does not
consume the others. This example uses the DROP TOS instruction twice to
clear the remaining arguments from the data stack.
push #MSG_CLR ; ( flags, *msg_p, len )
call clearFlags ; ( *msg_p, len, - )
drop TOS ; ( len, -- )
drop TOS ; ( -- )
...
clearFlags
...
ret ; return to caller
86 Neuron Assembly Language Instruction Statements