GE SRTP — GE Fanuc / Emerson PACSystems

SRTP (Service Request Transport Protocol) is the standard communication protocol for GE Fanuc / Emerson PACSystems / GE RX3i / RX7i / VersaMax series PLCs. It is a PLC family frequently encountered in the North American automation market (automotive, aerospace, power generation).

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Registration form entries

Field	What to enter	Example
IP address	IP of the PLC	192.168.0.150
Port	SRTP port	18245 (standard / changing it is not recommended)
Response timeout (request-timeout)	Response wait time (ms)	5000

GE PLCs communicate without a separate user name or password. SRTP communication must be enabled on the PLC side in Proficy Machine Edition or PAC Productivity Suite.

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PLC address notation for tags

GE PLCs denote memory areas in the form % + letter + number. This looks similar to Siemens, but the area letters differ.

Notation	Area	Remarks
%R100	Register Memory 100	Most common, 16-bit
%I100	Discrete Input 100	1 bit
%Q100	Discrete Output 100	1 bit
%T100	Temporary Reference 100	1 bit
%M100	Internal Memory 100	1 bit
%S100	System Reference	1 bit
%G100	Global Memory	1 bit
%AI100	Analog Input 100	16-bit
%AQ100	Analog Output 100	16-bit
%W100	Word Memory	16-bit

Combining words for 32-bit / floating point

One %R100 location is 16-bit. A 32-bit integer or float uses two locations (%R100 + %R101) combined, with the width specified via [format modifier].

Notation	Meaning
%R100	16-bit integer
%R100 + DW	32-bit integer (R100–R101)
%R100 + REAL	32-bit float (R100–R101)
%R100 + STR[10]	10-word (= 20 character) string

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Data type matching

Value in the PLC	Data type	Format modifier	PLC address example
Bit (I, Q, M, T)	Boolean	(leave empty)	%I100, %Q100, %M100
16-bit integer	Integer	(leave empty)	%R100, %AI100
16-bit unsigned	Integer	UI	%R100
32-bit integer	Integer	DW	%R100
32-bit unsigned	Integer	UDW	%R100
32-bit float (most common)	Float	REAL	%R200
64-bit float	Double	LREAL	%R300
String of N words	String	STR[N]	%R500

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Common problems and solutions

Symptom	Possible cause	Solution
"Connection refused"	SRTP port 18245 blocked, or SRTP disabled on the PLC	Enable SRTP communication in Proficy ME; open 18245 on the firewall
"Service request error"	Wrong area letter or number out of range	Use the correct area (%R / %I / %Q, etc.). Verify the number is within the PLC memory size
All values 0	Area mismatch (e.g. registered as %AI when it is %R)	Check in the Proficy reference table which area actually holds the data
32-bit values wrong	Format modifier not set	Specify DW (integer) / REAL (float)
Only Bool fails to read	Bool registered in the %R area	Use a bit area such as %I / %Q / %M / %T

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Frequently used examples

Tag name	PLC address	Data type	Format modifier
Pump running	%M100	Boolean	(leave empty)
Input signal	%I100	Boolean	(leave empty)
Output ON	%Q100	Boolean	(leave empty)
16-bit counter	%R100	Integer	(leave empty)
32-bit accumulated	%R200	Integer	DW
Pressure (float)	%R300	Float	REAL
Batch name (10 words)	%R500	String	STR[10]

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Next steps

• The reference table in Proficy Machine Edition / PAC Productivity Suite is the most accurate source of addresses.
• See the GE examples in Advanced — REST API.