1. Supported Areas

S7 driver supports the following memory areas. Addresses are case-insensitive.

Area Code	Name	Description	Address Format Example
DB	Data Block	Global Data Block	DB1.W10, DB10.INT20
I	Input	Digital Input	I0.0 (Bit), IB0 (Byte), IW0 (Word)
Q	Output	Digital Output	Q0.0 (Bit), QB0 (Byte), QW0 (Word)
M	Memory	Internal Flag/Intermediate Variable	M0.0 (Bit), MB0 (Byte), MW0 (Word)
V	V Memory	Mapped to DB1 (Common for S7-200 Smart)	V0.0 (Bit), VB0 (Byte), VW0 (Word)
T	Timer	Timer Current Value	T1, T10
C	Counter	Counter Current Value	C1, C20
DI	Instance DB	Instance Data Block	DI1.W0
L	Local	Local Data	LB0, LW0
DP	Peripherals	Direct Peripheral Access	DPB0, DPW0

Note

• V Area Mapping: In NG Gateway S7 driver, V area is mapped to DB1 by default. E.g., VB100 is equivalent to DB1.B100.
• DB Area Format: DB address must include block number, format is DB{BlockNo}.{Type}{Offset}.

2. Data Types and Prefixes (Transport Size)

The driver determines data read length and decoding method via Type Prefix in the address. Supports long naming and short naming (e.g., INT and I).

Type Name	Long Prefix	Short Prefix	Length (Byte)	Rust Type	Description
Bit	BIT	X	1/8	bool	Bit access (Must specify .bit index; carried as 1 byte on wire)
Byte	BYTE	B	1	u8	Single Byte (Convert on business side if i8 semantics needed)
Char	CHAR	C	1	char	Single Char (Write/Read as 1 byte code value)
Word	WORD	W	2	u16	Unsigned Word
Int	INT	I	2	i16	Signed Integer
DWord	DWORD	DW	4	u32	Unsigned Double Word
DInt	DINT	DI	4	i32	Signed Double Integer
Real	REAL	R	4	f32	Float
Time	TIME	T	4	chrono::Duration	IEC Time (ms); Note difference from Area T (Timer)
Date	DATE	-	2	chrono::NaiveDate	IEC Date (Driver decodes as date)
TimeOfDay	-	TOD	4	chrono::NaiveTime	Time of Day (ms), decoded as NaiveTime
S5Time	S5TIME	ST	2	chrono::Duration	S5 Format Time, decoded as Duration
DateTime	DATETIME	DT	8	chrono::NaiveDateTime	DATE_AND_TIME (BCD, 8 bytes)
DateTimeLong	DATETIMELONG	DTL	12	chrono::NaiveDateTime	DTL (12 bytes, S7-1200/1500)
String	STRING	S	256 (envelope)	String	STRING structure whole read (Latin-1): [max:u8][len:u8][payload...]
WString	WSTRING	WS	512 (envelope)	String	WSTRING structure whole read (UTF-16BE): [max:u16][len:u16][payload...]

Hint

• If type prefix is not specified (and no decimal point), default parses as Byte (e.g., M10 equivalent to MB10).
• If there is a decimal point but no type prefix (e.g., M10.2), auto parses as Bit.

3. Address Formats and Examples

The table below shows various common address spellings and their parsing results.

3.1 I/Q/M/V Area Examples

I/Q/M/V areas support three types of writing:

1. Legacy Address: Common shorthands in KepServer/Step7 like ID0/MD200/VD100 (Note: Some are not directly supported in NG Gateway and need migration).
2. NG Gateway Full Address: Use long type prefix (e.g., WORD/REAL/DINT), best readability.
3. NG Gateway Short Address: Use short type prefix (e.g., W/R/DI) or omit type by rule (Recommend explicit type declaration).

Legacy Address	NG Gateway Full Address	NG Gateway Short Address	S7 Data Type	Rust Type	Description
I0.0	IBIT0.0	IX0.0	Bit	bool	I Area, Byte 0, Bit 0 (Bit access must include .bit)
Q1.7	QBIT1.7	QX1.7	Bit	bool	Q Area, Byte 1, Bit 7
M10.5	MBIT10.5	MX10.5	Bit	bool	M Area, Byte 10, Bit 5
V100.0	DB1.BIT100.0	VX100.0	Bit	bool	V Area mapped to DB1.* in driver (Equivalent to DB1.X100.0)
IB0	IBYTE0	IB0	Byte	u8	I Area, Byte 0
QB10	QBYTE10	QB10	Byte	u8	Q Area, Byte 10
MB20	MBYTE20	MB20	Byte	u8	M Area, Byte 20
IW0	IWORD0	IW0	Word	u16	I Area, Unsigned 16-bit starting at Byte 0 (Big Endian)
QW4	QWORD4	QW4	Word	u16	Q Area, Unsigned 16-bit starting at Byte 4 (Big Endian)
MW10	MWORD10	MW10	Word	u16	M Area, Unsigned 16-bit starting at Byte 10 (Big Endian)
ID0	IDWORD0	IDW0	DWord	u32	I Area, Unsigned 32-bit starting at Byte 0 (Big Endian); Please use IDW*/IDWORD* for migration
MD200	MDINT200	MDI200	DInt	i32	M Area, Signed 32-bit starting at Byte 200 (Big Endian); Legacy MD* semantics is "4 Bytes", explicitly declare DI/DINT in this driver
MD200	MREAL200	MR200	Real	f32	M Area, IEEE-754 f32 starting at Byte 200 (Big Endian); If legacy MD* represents float, please use R/REAL
VD100	DB1.DWORD100	VDW100	DWord	u32	V Area (DB1) Unsigned 32-bit starting at Byte 100 (Big Endian); Legacy VD* please change to VDW* or directly use DB1.DW*

3.2 DB Area Examples

DB Area address must start with DB, followed by block number. Format: DB{BlockNo}.{Type}{Offset}.

Migration Reminder

NG Gateway current address parser (See ng-gateway-southward/s7/src/protocol/frame/addr.rs) does not support Siemens legacy "Combined Prefix" like DBX/DBB/DBW/DBD (e.g., DB1.DBD100). Please use NG Gateway Full/Short Address in the table below.

Legacy Address	NG Gateway Full Address	NG Gateway Short Address	S7 Data Type	Rust Type	Description
DB1.DBX0.0	DB1.BIT0.0	DB1.X0.0	Bit	bool	DB1, Byte 0 Bit 0 (Bit must be written as *.Xbyte.bit or *.BITbyte.bit)
DB10.DBB0	DB10.BYTE0	DB10.B0	Byte	u8	DB10, Byte 0
DB10.DBW2	DB10.WORD2	DB10.W2	Word	u16	DB10, Unsigned 16-bit starting at Byte 2 (Big Endian)
DB10.DBW4	DB10.INT4	DB10.I4	Int	i16	DB10, Signed 16-bit starting at Byte 4 (Big Endian)
DB1.DBD0	DB1.DWORD0	DB1.DW0	DWord	u32	DB1, Unsigned 32-bit starting at Byte 0 (Big Endian)
DB1.DBD4	DB1.DINT4	DB1.DI4	DInt	i32	DB1, Signed 32-bit starting at Byte 4 (Big Endian)
DB1.DBD8	DB1.REAL8	DB1.R8	Real	f32	DB1, IEEE-754 f32 starting at Byte 8 (Big Endian); Legacy DBD* only means "4 Bytes", must explicitly declare DW/DI/R in this driver
DB2.STRING0	DB2.STRING0	DB2.S0	String	String	S7 STRING Structure ([max:u8][len:u8][payload...], Latin-1), address should point to structure start offset
DB2.WSTRING100	DB2.WSTRING100	DB2.WS100	WString	String	S7 WSTRING Structure ([max:u16][len:u16][payload...], UTF-16BE), address should point to structure start offset
-	DB5.DATETIME0	DB5.DT0	DateTime	chrono::NaiveDateTime	8 Bytes DATE_AND_TIME (BCD)
-	DB5.DATETIMELONG0	DB5.DTL0	DateTimeLong	chrono::NaiveDateTime	12 Bytes DTL (S7-1200/1500); Different from DT, nanosecond field is 24-bit BE

Best Practices and Common Pitfalls

• Explicitly Declare Type: For production environment, recommend using short and explicit type prefixes (e.g., DB1.R8, MDI200), avoiding ambiguity from implicit Byte (e.g., M10).
• Bit Address must include .bit: E.g., QX1 will be judged illegal in driver, must be written as QX1.0 (See parser test cases).
• Legacy DBD/MD/VD only represents "4 Bytes": In NG Gateway syntax, must specify which of DW (u32) / DI (i32) / R (f32) it is.
• V Area is Syntactic Sugar for DB1: VB100 is equivalent to DB1.B100. When collaborating across teams/troubleshooting, writing DB1.* directly is usually more intuitive.
• STRING/WSTRING offset points to structure start: STRING/WSTRING variables in PLC contain length header (2/4 bytes). Driver reads and decodes the whole structure, offset should not point to the first character.
• Endianness and Alignment: Numeric types use Big Endian encoding per S7 convention. Recommend natural alignment by type (Word starts at even, DWord/Real starts at multiple of 4) to improve readability and reduce potential overhead on PLC side.

3.3 Timer / Counter Examples

Address	Type	Description
T1	Timer	Timer T1
C10	Counter	Counter C10