modsim is a very simple Modbus TCP device simulator deployed on cloud, which populates a few registers for each type of Coil / Discrete input / Input register / Holding register.
It is recommended to use modpoll to test with it, the example configuration is as following,
device,modsim001,1,,
poll,holding_register,40000,20,BE_BE
ref,value1,40000,uint16,rw
ref,value2,40001,uint16,rw
ref,value3,40002,uint16,rw
ref,value4,40003,uint16,rw
ref,value5,40004,int16,rw
ref,value6,40005,int16,rw
ref,value7,40006,int16,rw
ref,value8,40007,int16,rw
ref,value9,40008,uint32,rw
ref,value10,40010,uint32,rw
ref,value11,40012,int32,rw
ref,value12,40014,int32,rw
ref,value13,40016,float32,rw
ref,value14,40018,float32,rw
poll,coil,0,4,BE_BE
ref,coil1-8,0,bool,rw
ref,coil9-16,1,bool,rw
ref,coil17-24,2,bool,rw
ref,coil25-32,3,bool,rw
A docker image has been provided for user to directly run the program,
docker run -p 5020:5020 helloysd/modsim