AT903 VFD modbus register map

Hi all, 

After some success with modbus comms using pkuart and hm2_modbus (thanks to PCW for all the support) I'm minded to try talking to the VFD with modbus as well.  However the vfd is (cheap, amazon-sourced) model AT903 of the AT900 series, maker unknown, and although the manuals I've found show how to set it up for modbus comms they do not include any kind of register map. There's a parameter for '0=standard modbus 1=nonstandard modbus' and a number of other params related to serial comms, but that's it. 

Has anyone successfully talked to one of these over serial, or knows who make them, or has the register map? 


Andy

So I spent much of yesterday using Claude to help me figure out the AT903's modbus setup. I found and used OpenModScan from here: github.com/sanny32/OpenModScan along with a waveshare USB-RS485 adapter to communicate with the mystery VFD. I'd recommend OMS, it installed straightforwardly on my linuxcnc PC and proved easy enough for me to use as a newcomer to modbus. 

I found several versions of a manual that relates to the 'AT900 series' VFDs, (i.e. AT901 and AT903) some with odd unicode, have attached one of the more readable ones. 

I scanned about 16000 addresses in the modbus holding register range and found that there are around 16 blocks of used addresses, each starting at the beginning of 256-bit blocks, which correspond quite closely (identical in many cases) with the manual's function groups as coded e.g. P01.01 is at 0x0001, P17.00 at 0x1000. I've confirmed that I can write to some of those addresses as well as read them; I have not yet managed to find the address that accepts actual run and frequency setpoint commands - the freq. setpoint address shown in the manual is read-only.  

Spreadsheet is attached - copies of the function groups per the manual, next to their modbus addresses, in case this is useful to anyone else.

Anyone with time to have a quick look, who has a deeper familiarity with modbus standards, I'd be grateful to get some idea of the most likely command register addresses.