XinJe_PLC_Skill/references/soft-elements-and-special-relays.md

Soft Elements and Special Relays

Use this reference for Xinje XD/XL/XG soft-element questions, especially SM0, SM2, the common misconception around M8000, special auxiliary relays, special data registers, and soft-element allocation tables.

Source priority:

• Xinje official download center, XD、XL系列可编程控制器用户手册【基本指令篇】, version 1.6.1, updated 2026-06-26.
• Xinje official download center, XG系列PLC用户手册【基本指令篇】, version 1.0, updated 2024-12-16.
• When exact ranges differ by PLC model, ask for the specific CPU model and check the model’s soft-element table in the original PDF.

M8000 Clarification and SM0 Naming

For current Xinje XD/XL/XG documentation, the always-on run bit is documented as SM000 / SM0, not M8000.

Important accuracy rule: do not state that M8000 exists as a Xinje XD/XL/XG special relay, and do not state that M8000 = SM000. The bundled XD/XL and XG basic-instruction manuals document SM000 as the PLC running always-ON coil. They do not define M8000 as a run-state bit.

If XDPPro or a project accepts an address such as M8000, treat it as a normal M auxiliary relay address if that address is within the model’s valid M range. It is then user logic memory, not a system always-ON relay. A normal M coil only has the value written by the program/HMI/monitoring operation.

Use these Xinje XD/XL/XG devices instead:

Need	Use	Meaning
PLC running always-ON	SM000 / SM0	ON while PLC is in RUN.
PLC running always-OFF	SM001 / SM1	OFF while PLC is in RUN.
First scan ON pulse	SM002 / SM2	ON only during the first scan after PLC starts running.
First scan OFF pulse	SM003 / SM3	OFF only during the first scan after PLC starts running.

The XG manual contains an old XC-series communication example using M8002, but the XG special auxiliary relay appendix itself lists SM000 through SM003 for run and first-scan states. Treat those M800x appearances as example/migration residue, not as XD/XL/XG special-relay definitions.

Core Soft Elements

Element	Purpose	Key notes
X	Input relay	Physical input points. X/Y addresses use octal-style numbering such as X0~X7, X10~X17. Expansion modules commonly start from X10000, BD from X20000, ED from X30000, depending on model.
Y	Output relay	Drives external loads. Y addresses also use octal-style numbering. Extra internal Y points beyond physical outputs may be usable as normal internal coils/contacts.
M, HM	Auxiliary relay	Internal relay bits only; they do not read external inputs or directly drive loads. HM is retentive. If an address like M8000 is valid on the selected model, treat it as this ordinary M memory area, not as a special run-state relay.
SM	Special auxiliary relay	System/special bit. Use for run state, first-scan pulse, clock pulses, communication status, error flags, etc. Avoid using as ordinary memory unless the manual marks it available.
S, HS	State relay	Used for step ladder / process steps. If not used as step numbers, they can act like normal contacts/coils. HS is retentive.
T, HT	Timer	Timers support 1 ms, 10 ms, and 100 ms time bases depending on timer range. Accumulative timers retain current value while the drive input is off; non-accumulative timers clear when drive input is off.
C, HC	Counter	Internal counters are scan-cycle based; high-speed counters are assigned to specific input points and work independently of PLC scan cycle.
D, HD	Data register	16-bit data registers. Adjacent registers can be combined for 32-bit and 64-bit operations. HD is retentive.
SD, HSD	Special data register	System/special word register. Use for scan time, clock, communication results, error codes, module state, and other system data.
FD, SFD	FlashROM register	Retentive Flash storage. Frequent writes can wear Flash; avoid high-frequency writes. SFD contains special Flash parameters.
FS	Secret register	Flash-backed register intended for IP protection. It can be written but cannot be read back normally; read returns 0. Commonly FS0~FS47, but verify online by model.

Addressing Rules To Remember

• X and Y use octal-style point numbering in the base unit, for example Y0~Y7, Y10~Y17.
• M, HM, S, HS, T, HT, C, HC, D, HD, FD, FS, SM, and SD use decimal numbering unless a specific table says otherwise.
• A word can be built from 16 continuous bit elements by prefixing D: DM10 means the 16-bit word made from M10~M25; DY0 means the 16-bit word made from Y0~Y17.
• Timer/counter identifiers can act as either bit contacts/coils or word current values depending on the instruction. Example concept: LD T11 treats T11 as a bit contact; MOV T11 D0 treats it as the timer current-value word.
• Register bit addressing uses Dn.m, where m is the bit index. The manual describes 0 <= m <= 63; in practice, confirm instruction width and target model.
• Offset addressing uses forms like D10[D0], Y0[D0], or DX2[D0]. Only XDH/XLH support SFD offset addressing in the referenced XD/XL manual.

Frequently Used Special Auxiliary Relays

Initial/run state:

Device	Function
SM000	PLC running always-ON coil.
SM001	PLC running always-OFF coil.
SM002	Initial positive pulse; ON only during the first scan cycle after PLC starts running. Use for one-shot initialization.
SM003	Initial negative pulse; OFF only during the first scan cycle after PLC starts running.
SM004	PLC runtime error indication; supported on firmware V3.4.5 and above in the referenced XD/XL manual.
SM005	Low battery alarm on supported non-EtherCAT bus models.

Clock pulses:

Device	Function
SM011	10 ms cycle pulse.
SM012	100 ms cycle pulse.
SM013	1 s cycle pulse.
SM014	1 minute cycle pulse.

Arithmetic flags:

Device	Function
SM020	Zero flag; ON when add/subtract result is 0.
SM021	Borrow flag; ON on lower-limit overflow.
SM022	Carry flag; ON on upper-limit overflow.

PC/mode and step flags:

Device	Function
SM030	PLC initialization / restore factory setting. Treat as potentially destructive.
SM032	Clear retentive storage for HM, HS, HT, HC, HD. Treat as potentially destructive.
SM034	Disable all outputs. The software may still show pulse changes, but actual outputs are inhibited.
SM040	Step process executing flag.

Interrupt and high-speed counter groups:

• SM050~SM069: disable input interrupts.
• SM070~SM089: disable timer interrupts.
• SM090: disable all interrupts.
• SM099: high-speed ring counter enable; when ON, SD099 increments every 0.1 ms and cycles 0 to 32767.
• SM100~SM109: HSC0, HSC2, ... HSC18 100-segment count-completion flags.
• SM110~SM119: HSC0, HSC2, ... HSC18 direction flags.
• SM120~SM129: HSC0, HSC2, ... HSC18 error flags.
• SM130~SM139: HSC0, HSC2, ... HSC18 overflow flags.

Communication groups:

• SM140~SM193: serial-port communication status.
• For each port group, Modbus executing, X-NET executing, free-format sending, and free-format receive-complete flags repeat by port.
• Example pattern: serial port 0 uses SM140 Modbus executing, SM141 X-NET executing, SM142 free-format sending, SM143 free-format receive complete.

Error flags:

Device	Function
SM400	I/O error.
SM401	Expansion module communication error.
SM402	BD/ED communication error.
SM403	FROM/TO instruction error flag.
SM404	PID instruction error flag.
SM405	No user program / internal code checksum error.
SM406	User program error.
SM407	SSFD checksum error.
SM408	Memory error; cannot erase or write Flash.
SM409	Operation/arithmetic error.
SM410	Offset overflow error; offset exceeds soft-element range.
SM411	FOR-NEXT overflow error.
SM413	Encryption verification error.
SM414	Flash register data error.
SM415	RTC time/date verification failed.

Frequently Used Special Data Registers

Device	Function
SD005	Battery voltage display register. On supported models, 3.1 V displays 100; below 2.5 V displays 0.
SD010	Current scan cycle, unit 100 us.
SD011	Minimum scan time, unit 100 us.
SD012	Maximum scan time, unit 100 us.
SD013~SD019	Clock data: second, minute, hour, day, month, year, weekday.
SD020~SD031	Model/version information and applicable host software version fields.
SD040	Current executing step S number.
SD099	High-speed ring counter value, enabled by SM099.
SD100~SD109	Current HSC segment for HSC0, HSC2, ... HSC18.
SD120~SD129	HSC error information for HSC0, HSC2, ... HSC18.
SD140~SD199	Communication results. SD140 is Modbus read/write result for serial port 0 in the referenced XD/XL manual.
SD400~SD414	Detailed error types corresponding to SM400~SM414.
SD500~SD516	Expansion module / BD / ED status.

SFD Flash Parameters

Use SFD carefully: values often affect hardware behavior, some require power cycle, and Flash writes should not be frequent.

• SFD0*: input filter time, default 10 ms.
• SFD2*: watchdog action time, default 200 ms.
• SFD3*: special function configuration word; supported from firmware V3.4.6b in the referenced XD/XL manual.
• SFD320~SFD329: HSC multiplier settings for HSC0, HSC2, ... HSC18.
• SFD330: 100-segment HSC absolute/relative selection bits.
• SFD331: 100-segment HSC interrupt loop bits.

The * marker in the manual means the setting requires PLC power cycle to take effect.

Answering Checklist

When a user asks about M8000, special relays, or soft elements:

1. Clarify PLC series if it affects the exact table: XD, XL, XG, XC, XDQ/XLQ, or XS.
2. For XD/XL/XG, answer that M8000 is not a documented special relay and is not equivalent to SM000/SM0. If the software accepts M8000, treat it as ordinary M auxiliary relay memory within the valid model range.
3. Use SM002/SM2 for one-time initialization at first scan.
4. Warn before suggesting SM030, SM032, SFD writes, output disable, forced outputs, online changes, or any operation that changes machine state.
5. For model-specific address ranges, check the original PDF soft-element table instead of guessing.