[etherlab-users] Accessing same PDO for both read and write

Thomas Nelson gcsnh at granitecomputersciences.com
Thu Jan 24 16:00:59 CET 2013

On Jan 23, 2013, at 11:21 PM, Graeme Foot wrote:

> Hi,
> I don't know the answer to the question, but as a workaround you could set up reading the value via PDO and write the value via an SDO.  Writing via SDOs take approx 30ms for CoE.
> Regards,
> Graeme.
> From: etherlab-users-bounces at etherlab.org [mailto:etherlab-users-bounces at etherlab.org] On Behalf Of Thomas Nelson
> Sent: Thursday, 24 January 2013 16:15
> To: etherlab-users at etherlab.org
> Subject: [etherlab-users] Accessing same PDO for both read and write
> All,
> My client has a robotics system using Copley Controls Accelnet Plus drives with a digital input-triggered capture capability that we're trying to use for positioning calibration.  This feature requires the ability to map the same slave CoE object for both read to detect the capture event and write to subsequently rearm the trigger.  Mapping this object to both Tx and Rx PDOs appears to work correctly from the PDO mapping info returned from the master.  However, when I attempt to register the corresponding mapped PDO entries in the domain, I get the same domain offset for both PDOs, preventing the application from managing them independently.
> The ecrt_slave_config_reg_pdo_entry() function doesn't have an argument to distinguish the direction of the PDO mapping, so is this capability not supported by the master?
> We're using the 1.5.0 release.

We had in fact discussed this as a possible alternative, but were concerned that the SDO latency (which we didn't know previously - thanks!) could prevent the trigger from being rearmed quickly enough to avoid missing a subsequent event at the target motion rates.  The system uses optical sensors for this calibration that generate rising and falling edge events that must be detected, and the r/w object in question handles trigger rearming for both types of events.

Best regards,

Tom Nelson
Consulting Engineer
Granite Computer Sciences, LLC
(603) 672-8525

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