FOCUS Software Engineering made their command line utility "modpoll"
available as free software.
The utility "modpoll" is a command line based Modbus master simulator and
test utility. It's functionality is based on the FieldTalk(tm) Master
Protocol Pack Modbus(R)/C Edition libraries.
Modpoll can be downloaded from www.focus-sw.com section Modbus->Modpoll
FOCUS Software Engineering