Fanuc System Variables

Fanuc system variables (the #-numbers) are how a custom macro reads and writes the control’s internal state — tool offsets, work offsets, live axis positions, probe results, modal codes, timers, and alarms. A part program treats them like any other variable: read one into a general-purpose variable, do arithmetic, and (where the variable is writable) assign a new value back. This is the mechanism behind every probing routine, tool-breakage check, and adaptive macro on a Fanuc control.

How the Numbering Is Organized

The number itself tells you what family a variable belongs to. Once you know the map, an unfamiliar #-number stops being a lookup exercise:

Range	Family
#1–#33	Local variables & macro call arguments
#100–#999	Common (general-purpose) variables
#2001–#2800, #10001–#13999	Tool offsets
#3000–#3902	Alarms, timers, control switches, counters
#4001–#4130	Modal information (active G-codes and addresses)
#5001–#5108	Positions (previous block, machine, work, skip, deviation)
#5201–#5328, #7001–#7948	Work offsets (external, G54–G59, G54.1 P1–P48)

Complete Reference

The R/W column is the part most tables leave out — it tells you whether a macro can assign to the variable (R/W or W) or only read it (R). Writing to a read-only variable raises an alarm.

Generation Notes

The table above uses the classic 8-axis numbering of the 16i/18i era, which most shop-floor references assume. Where the manuals genuinely differ by control family:

One 16i/0i-era wrinkle: #5201–#5328 (and the even older per-axis aliases #2500–#2806) require the workpiece-coordinate-system option on those controls. The #2500-block work-offset aliases were dropped from the 30i numbering — don’t confuse them with the #2001-block tool offsets.

Read-Only vs Read/Write at a Glance

The rule of thumb: variables that report machine state (positions, modal codes, clock, mirror status) are read-only; variables that hold setup data (offsets, common variables, counters, timers) are writable. Getting this wrong is the classic source of “why won’t it write?” confusion — e.g. #5041 (where the axis is) cannot be assigned, but #5221 (where G54 points) can.

Named System Variables (30i / 0i-F / Plus)

On the 30i family, every system variable in the tables above also has a name. The format is [#_NAME] for scalars and [#_NAME[i]] for indexed families — the whole reference, # included, sits inside square brackets. A name begins with an underscore followed by up to seven uppercase letters, numerics, or underscores, and the subscript can be any expression, with a non-integer result rounded off ([#_ABSIO[1.4999999]] reads #5001; [#_ABSIO[1.5]] reads #5002). Names have been there since the first 30i (Model A), and they beat raw numbers on two counts: they read like what they are, and they survive numbering changes — [#_WZG54[3]] is G54’s third axis whether the control maps it at #5223 or at #100353 in the 50-axis range, and the tool-offset names follow the wear/geometry meaning even when the V15 parameter bit swaps which #2xxx range holds which. The control also polices them: a misspelled or unregistered name raises alarm PS1098 (“NO VARIABLE NAME”), and an invalid subscript raises PS1099.

The curated table below covers the names a mill macro actually reaches for; the full list in the B-64724EN manual runs to well over a hundred.

Side by side, the number form and the name form of the same reads and the same probe write (this is the “touch off and set zero” pattern worked in full in the next section — Z is axis 3, so [#_WZG54[3]] is #5223 and [#_ABSKP[3]] is #5063):

(READ G54 Z - NUMBER FORM, THEN NAMED FORM)
#101 = #5223
#101 = [#_WZG54[3]]                          (INDEX 3 = Z, THE 3RD AXIS)

(PROBE TOUCH-OFF WRITE, NAMED FORM)
G90 G31 Z-25. F50.                           (FEED DOWN UNTIL THE PROBE TRIPS)
[#_WZG54[3]] = [#_WZG54[3]] + [#_ABSKP[3]]   (SHIFT G54 Z BY THE SKIP Z)
G00 Z25.                                     (RETRACT)

Because the subscript takes any expression, the indirect-addressing tricks later in this article carry straight over — [#_ABSKP[#500*2]] is legal. The lathe-side names (#_OFSXW, #_OFSZG, #_WKSFTX and kin) are mapped in the Fanuc Turning System Variables article.

Reading & Writing System Variables in a Macro

Read the current work coordinate and motion mode, then decode them:

#100 = #4001   (active motion mode: 0=G00, 1=G01, 2=G02, 3=G03)
#101 = #4014   (active work coordinate: 54-59)
#102 = #5041   (current X in the work coordinate system)
#103 = #5021   (current X in machine coordinates)

Probe a surface and write the result to a work offset. This is the core “touch off and set zero” pattern: feed down with G31 until the probe trips, then shift the G54 Z offset (#5223) so the touched face becomes Z0 in that work coordinate system. (#5061–#5068 hold the skip position in work coordinates; the axis order is X, Y, Z…, so Z is #5063.)

(TOUCH TOP OF PART, SET IT AS G54 Z0)
G90 G31 Z-25. F50.        (feed down until the probe trips)
#5223 = #5223 + #5063     (shift G54 Z so the touched face = Z0)
G00 Z25.                  (retract)

Measure a tool on a tool setter and write its length offset. The same skip mechanism, but the write target is a tool geometry offset, addressed indirectly so one macro serves every tool. #500 holds the calibrated trigger height of the setter (a retained common variable, set once during calibration):

(MEASURE TOOL LENGTH ON A TOOL SETTER)
#1 = 5                      (tool / H number being measured)
G91 G31 Z-400. F200.        (first touch, fast)
G01 Z2.                     (back off)
G31 Z-4. F30.               (second touch, slow, for repeatability)
#[11000 + #1] = #5063 - #500  (geometry offset = skip Z minus setter height)
G91 G28 Z0.                 (home Z)

Indirect addressing also works on the read side — here, checking the geometry length offset for whatever H-code is currently active:

#104 = #[11000 + #4111]   (geometry length offset for the active H number)
IF [#104 GT 6.0] GOTO 10  (branch if the tool is unexpectedly long)

Gotchas Worth Knowing

• Look-ahead buffering. The control reads blocks ahead of the one executing. A macro block that reads position or modal state can be evaluated before the preceding motion finishes — and a block already in the buffer keeps the old value of a work offset you just wrote. Where the read/write must be synchronized with motion, force the buffer to drain first (a G04 dwell or a G53 positioning block are the common idioms).
• Read positions with the axes stopped. The manuals mark #5021–#5028 and #5041–#5048 as “read operation during movement: disabled” — because of the buffering (pre-read) function, a value read mid-move is not guaranteed to be the expected one. The exception is the skip block: #5061–#5068 are latched at the instant the G31 input trips, which is exactly why probing macros read those instead of #5041.
• Tool offset numbering depends on the memory type — and one parameter bit. The five-digit #10001+ blocks are the safe choice: they exist on every memory type and cover offsets 1–999. The four-digit #2001+ numbers are aliases for the first 200 offsets only, and what they mean shifts with memory type (on type A, #2001 is the whole offset; on B/C it is the wear register by default). On top of that, bit 3 (V15) of parameter 6000 swaps the wear/geometry assignment across the whole map to match FS15 conventions — and some builders ship it set. Write a known value from MDI and read it back before trusting hard-coded numbers.
• The null variable #0 is not zero. An unset (vacant) variable equals #0, and IF [#7 EQ #0] (is it vacant?) behaves differently from IF [#7 EQ 0] (is it zero?). A vacant variable used in arithmetic is treated as 0, which silently masks a missing macro argument — test against #0 when an argument is optional.
• #3000 stops the program; #3006 pauses it. Use #3000 = n (TEXT) for a hard fault (operator must reset) and #3006 = 1 (TEXT) for a planned operator interaction (cycle start continues).

▶ Try these in the Macro Playground — pick the Fanuc control, type a macro, set the system-variable inputs (like #5063), and watch the values update live as it runs.

See also: Reading & Writing System Variables for the same probe-to-offset chain on every control, Modal & Position Data for the #4001/#5001 families in depth, Tool Offset Variables for offset-memory details, and Custom G/M Cycles for packaging these reads and writes into a reusable cycle.

References

• FANUC, Series 30i/31i/32i-MODEL B Plus Operator’s Manual (Common to Lathe System / Machining Center System), B-64724EN/01, Ch. 16 “Custom Macro”.
• FANUC, Series 30i/31i/32i-MODEL A User’s Manual (Common to Lathe System / Machining Center System), B-63944EN/03, Ch. 16 “Custom Macro”.
• FANUC, Series 16i/18i/160i/180i-MODEL B Operator’s Manual (Machining Center), B-63534EN/02, Ch. 15 “Custom Macro”.
• FANUC, Series 0i-MODEL B Operator’s Manual (Machining Center), B-63844EN/02, Ch. 15 “Custom Macro”.
• Peter Smid, Fanuc CNC Custom Macros, Industrial Press, 2004.