Sinumerik R-Parameters & System Variables

If you know Fanuc Macro B, Sinumerik does everything #-variables do — it just splits the job in two: R-parameters are your free scratch variables (like #100–#999), and $-prefixed system variables are named reads/writes into the control (like #3000–#5000-series). The names look intimidating until you learn the two-letter decode — then they're easier to remember than Fanuc's numbers.

R-Parameters (Arithmetic Parameters)

R0–R99 (expandable via machine data MD28050 $MC_MM_NUM_R_PARAM) are channel-specific REAL variables, freely available to the programmer. Unlike Fanuc's volatile #100-series, R-parameters are retentive — they survive power-off and are included in data backups. There is also a global flavor, RG[n], shared across channels.

Item	Sinumerik	Fanuc equivalent
Scratch variables	`R0`–`R99` (or `R[n]`)	`#100`–`#199` (but R-params persist like `#500`s)
Global across channels	`RG[n]`	— (Fanuc commons are already control-wide)
In synchronized actions	`$R[n]` or `$Rn`	—
Type	DOUBLE (REAL)	Same — floating point
Count	Set by `MD28050 $MC_MM_NUM_R_PARAM`	Fixed by option/model

Assignment and math are plain infix — no brackets-around-everything like Fanuc:

R1 = 10.5              ; simple assignment
R2 = R1 * 2 + SIN(30)  ; expressions read naturally
R[R2] = 1              ; indirect addressing (Fanuc: #[#102]=1)
X=R1 Y=-R2 F500        ; use directly in motion blocks

Decoding the $-Prefix Naming Scheme

This table is the key to the whole system. Every system variable is $ + data class + scope letter + _NAME. Once you can decode $AA_IM[X] as "runtime data, axis-specific, position (I) in machine coords (M), for X" you can sight-read most Siemens programs.

1st letter (data class)	Meaning	Fanuc analogy
`$M`	Machine data (configuration, protected)	Parameters
`$S`	Setting data (operator-adjustable)	Settings
`$T`	Tool data (offsets, tool type)	`#2001`+ / `#10001`+ offset variables
`$A`	Runtime (current) system data	`#3000`–`#5000`-series reads
`$V`	Service data (e.g. raw encoder actual values)	Diagnostic screens
`$P`	Program-run data (evaluated during block preprocessing)	Modal `#4001`+ variables
`$R`	R-parameter (synchronized-action notation)	`#100`-series

2nd letter (scope)	Meaning	Examples
`N`	NCK-global (whole control)	`$MN_`, `$SN_`, `$AN_`
`C`	Channel-specific	`$MC_`, `$SC_`, `$AC_`, `$TC_`
`A`	Axis-specific (takes an `[axis]` index)	`$MA_`, `$SA_`, `$AA_`, `$VA_`

So $AA_IM[X] = runtime + axis-specific + IM (position in the Machine coordinate system) for the X axis, and $AA_IW[X] is the same thing in the Workpiece coordinate system. A few exceptions carry no scope letter: $A_YEAR (global runtime data) and the $P_ family. Note: reading a $A.../$V... runtime variable in a part program forces an implicit preprocessing stop (like STOPRE) so the value is current — expect a brief pause in look-ahead.

System Variables Worth Knowing

The 828D lists manual documents thousands; these are the ones a programmer actually reads or writes. Axis-indexed variables take the axis name: $AA_IW[X].

Variable	What it is	Fanuc equivalent
Position
`$AA_IW[ax]`	Current position, workpiece coordinates (setpoint)	`#5041`–
`$AA_IM[ax]`	Current position, machine coordinates (setpoint)	`#5021`–
`$VA_IM[ax]`	Encoder actual value, machine coordinates	—
`$P_EP[ax]`	Programmed end position of current block	`#5001`–
`$AA_MW[ax]` / `$AA_MM[ax]`	Measured probe trigger position, WCS / MCS	`#5061`– skip position
Tool
`$P_TOOLNO`	Active tool number (T)	`#4120`
`$P_TOOL`	Active cutting edge (D number)	`#4107`
`$P_TOOLP`	Last programmed tool number (no magazine mgmt)	—
`$TC_DP1[t,d]`	Tool type of tool t, edge d	—
`$TC_DP3[t,d]`	Tool geometry — length 1	`#2001`+ / `#11001`+
Work Offsets & Frames
`$P_UIFR[n]`	Settable work offset frame n (G54 = `$P_UIFR[1]`, active on G54–G599)	`#5221`– / `#7001`–
`$P_UIFRNUM`	Number of the active settable frame	`#4014` (modal WCS group)
`$P_IFRAME`	Active settable frame (the live G54…)	—
`$P_PFRAME`	Programmable frame (TRANS/ROT)	`#5201`– (G52-ish)
`$P_ACTFRAME`	Total active frame (everything chained)	—
Feed & Spindle
`$P_F`	Programmed path feed	`#4109`
`$AC_VACTW`	Actual path velocity in the WCS	—
`$P_S[n]`	Programmed speed of spindle n	`#4119`
`$AA_S[n]`	Current speed of spindle n	—
`$AC_OVR`	Path override (writable in synchronized actions)	—
`$AC_MSNUM`	Number of the current master spindle	—
Modal & Status
`$P_GG[n]`	Active G function of G group n	`#4001`–`#4022`
`$AC_ALARM_STAT`	Alarm response status (bit-coded: stop, NOREADY…)	`#3000`-adjacent status
Time & Part Counters
`$A_YEAR` / `$A_MONTH` / `$A_DAY`	System date	`#3011`
`$A_HOUR` / `$A_MINUTE` / `$A_SECOND`	System time	`#3012`
`$AC_TIME`	Seconds since block start	`#3001`-ish
`$AC_CYCLE_TIME`	Execution time of the selected NC program	—
`$AC_OPERATING_TIME` / `$AC_CUTTING_TIME`	Total AUTO runtime / machining time	—
`$AC_TIMER[n]`	User timer n (set to start value; `-1` stops it)	—
`$AC_ACTUAL_PARTS`	Parts machined this run (auto-resets at target)	`#3901`
`$AC_REQUIRED_PARTS`	Part count target	`#3902`
`$AC_TOTAL_PARTS`	Total parts since start time	—

GUD — Global User Data

GUD is Siemens' answer to "I wish #510 had a name." Instead of memorizing that #510 holds your probe diameter, you define a retentive variable called PROBE_DIA in a GUD block — a definition file loaded onto the control (828D reserves blocks for Siemens cycles, the machine builder, and the end user). The number of available GUD modules is set by machine data $MN_MM_NUM_GUD_MODULES.

; In a user GUD definition file:
DEF NCK REAL PROBE_DIA        ; global to the whole control
DEF CHAN INT FIXTURE_ID       ; per channel

; Then in any program, by name:
PROBE_DIA = 6.0
IF FIXTURE_ID == 2 GOTOF OP20

Compared to Fanuc #500–#999 permanent commons: same persistence, but typed (REAL, INT, BOOL, AXIS, CHAR…), named, and scoped. For synchronized actions there is a pre-built set in the GUD2 block — SYG_RM[n] (REAL), SYG_IM[n] (INT), SYG_BM[n] (BOOL) — sized by machine data such as $MN_MM_NUM_SYNACT_GUD_REAL.

Worked Examples

Capture the current work-coordinate position into R-parameters (the Siemens version of reading #5041–#5043):

R1 = $AA_IW[X]   ; current X, work coords
R2 = $AA_IW[Y]   ; current Y
R3 = $AA_IW[Z]   ; current Z
MSG("Z WORK POS: " << R3)
M0               ; hold so you can read it

Branch on the active tool — e.g. refuse to run a probing routine unless the probe (T9) is in the spindle:

IF $P_TOOLNO <> 9 GOTOF WRONG_TOOL
; ... probing moves ...
GOTOF DONE

WRONG_TOOL:
MSG("LOAD PROBE T9 - ACTIVE TOOL IS T" << $P_TOOLNO)
M0

DONE:
M17

Nudge the G54 Z origin from inside a program — the equivalent of writing to #5223. $P_UIFR[1] is the G54 frame; index by axis and component (TR = translation):

$P_UIFR[1,Z,TR] = $P_UIFR[1,Z,TR] - 0.05  ; shift G54 Z down 0.05
G54                                        ; re-select to activate the change

References

Siemens, SINUMERIK 828D System Variables Lists Manual (08/2018), Siemens AG.
Siemens, SINUMERIK Programming Guide: Job Planning, Siemens AG.