Experimental Physics and
Industrial Control System

Hi Dominique,

Sorry for the delay in replying to this, I was on vacation.

I think an easier solution to this problem is to use 2 calc records to
convert the 32-bit integer to 2 16-bit integers, and write those to the
Modbus driver using function 6.  Then you don't have to write any C
code, just a simple database.

PowerSupply (longout) -> calc1 (16 LSB) -> longout1 -> Modbus
                      -> calc2 (16 MSB) -> longout2 -> Modbus

I don't recommend modifying the driver, because a 32-bit integer is not
a standard Modbus data type, and we could end up with all sorts of
modifications for non-standard data types.

Mark


> -----Original Message-----
> From: [email protected] 
> [mailto:[email protected]] On Behalf Of Touchard Dominique
> Sent: Wednesday, September 19, 2007 8:44 AM
> To: [email protected]
> Subject: Use of waveform records
> 
> Hi,
> 
> we are working on/with the Epics modbus tcp driver written by Mark
> Rivers. We need to write a 32 bits integer value in a power supply
> command control interface.  First we thought to write an asyn32Int
> record with the number 6 modbus function.  Immediatly, we saw that the
> driver uses the number 6 modbus function which works only on 
> a 16 bits word.
> 
> After reading the Modbus Driver Support documentation, we saw that we
> have to use a two value length waveform record.
> 
> First question : is this correct ?
> 
> Second question : do we have to use the gensub record to manipulate
> values inside a waveform record ? In this case, is there any example
> that shows how to do this ? Could somebody send us an example 
> on this ?
> 
> Third question : Is a bad idea to modify the modbus driver in the goal
> to write a asyn32Int 32 bits integer record with the  number 16 modbus
> function ?
> 
> Thanks for your help .
> 
> Dominique Touchard.
> 
> 

Replies:

RE: Use of waveform records Mark Rivers

References:

Use of waveform records Touchard Dominique

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