EPOS2 Application Notes Collection - Maxon Motor
EPOS2 Application Notes Collection - Maxon Motor
EPOS2 Application Notes Collection - Maxon Motor
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USB or RS232 to CAN Gateway<br />
Command Translation<br />
11.4 Command Translation<br />
The USB/RS232 command set is designed approximate to CANopen services. All USB/RS232 commands<br />
have a directly corresponding service in the CAN network, thus simplifying the gateway functionality.<br />
Between two subsequent USB/RS232 commands, no data must be stored or buffered, thus minimizing<br />
Gateway’s memory use. All received data are directly forwarded to the CAN bus.<br />
USB/RS232 Command<br />
CANopen Service<br />
ReadObject Initiate SDO Upload / Expedited Transfer<br />
InitiateSegmentedRead Initiate SDO Upload / Normal Transfer<br />
SegmentRead Upload SDO Segment<br />
WriteObject Initiate SDO Download / Expedited Transfer<br />
InitiateSegmentedWrite Initiate SDO Download / Normal Transfer<br />
SegmentWrite Download SDO Segment<br />
SendNMTService NMT Service<br />
ReadLSSFrame LSS Service<br />
SendLSSFrame LSS Service<br />
Table 11-157<br />
Command Translation – USB/RS232 to CANopen Service<br />
11.5 Limiting Factors<br />
The number of segments has a big influence on the data exchange performance. Exchanging data<br />
directly with a device connected to RS232 (no gateway), a data segment can transfer up to 63 Bytes per<br />
command, thus for 1kB of data, 17 commands must be sent. Compared to sending data to a device<br />
addressed via gateway, 147 commands must be sent. CANopen services (normal transfer) allow only 7<br />
bytes to be transferred in a segment. Therefore, the CANopen segment limits also the RS232 segment.<br />
Please keep in mind; the gateway is not capable of buffering data nor to split data into several CANopen<br />
services.<br />
Considering the segment size, CANopen is the limiting factor for the communication performance. Considering<br />
the bit rate of the two field buses, the RS232 interface is the limiting factor. Communication via<br />
gateway cannot take advantage of the CAN bus’ high bit rate, it is limited by the RS232’s slow bit rate<br />
and the small CANopen segment size.<br />
Description USB Protocol RS232 Protocol CANopen<br />
USB to<br />
CANopen<br />
Gateway<br />
RS232 to<br />
CANopen<br />
Gateway<br />
Max. bit rate 1 MBit/s 115.2 kBit/s 1 MBit/s 1 MBit/s 115.2 kBit/s<br />
Max. segment<br />
size<br />
63 Bytes 63 Bytes 7 Bytes 7 Bytes 7 Bytes<br />
Conclusion<br />
Transfer Rate Fast Slow Fast Fast Slow<br />
Segment Size Big Big Small Small Small<br />
Table 11-158<br />
USB or RS232 to CAN Gateway – Limiting Factors<br />
However, these limiting factors must be put into perspective, because most of the elements in the<br />
Object Dictionary are 32-bit parameters, or even smaller. Thus, segmented transfer is used very rarely.<br />
Segmented transfer will only be used to read the data recorder’s data buffer or for firmware download.<br />
maxon motor control<br />
<strong>EPOS2</strong> Positioning Controllers Document ID: rel3956 11-167<br />
<strong>EPOS2</strong> <strong>Application</strong> <strong>Notes</strong> <strong>Collection</strong> Edition: April 2013<br />
© 2013 maxon motor. Subject to change without prior notice.
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