Thank you, Mark, for your prompt reply. Most helpful. I do have a little modbus A-D RTU card and an RS485 card for the PC on which to test the actual modbus protocol, but Modsim looks to be worth a try and may well get me going rather quicker.
Meanwhile, let me disclose a particular issue here.
The ABB gas analyser from which I want to log data returns IEEE754 32bit data over modbus.
I am struggling to find an elegant way of converting the 32 bits, received as 4 bytes, to decimal.
I would appreciate any advice on this particular challenge!
The analyser is a replacement for just one of a number of analog instruments which we read using the HP/Agilent/Keysone Data Acquisition & Switch Unit 34970A with HPIB communication, so it would be very handy to solve this within the HP/HTBasic code which has run our system since 1989.
Thak you once again.