Rockwell Automation 20A PowerFlex 70EC/700VC - Manual (Page 42)

38 DPI
Peer-to-Peer operation
Peer-to-Peer messaging allows two devices to communicate directly rather than
through the master or host (e.g. drive). They are the same priority as C/S messages
and will occur in the background. If an LCD HIM is attached, it will be able to
directly access peripheral parameters (e.g. communication adapter parameters)
using Peer-to-Peer messages.
Peripheral devices will be scanned at a 10ms rate. Drive status messages will be
produced at a 5ms rate, while peripheral command messages will be accepted (by
the drive) as they occur (e.g. change of state). Based on these timings, the following
worst case conditions can occur (independent of the baud rate and protocol):
•
Change of peripheral state (e.g. Start, Stop, etc.) to change in the drive – 10ms
•
Change in reference value to change in drive operation – 10ms
•
Change in Datalink data value to change in the drive – 10ms
•
Change of parameter value into drive – 20ms times the number of attached
peripherals
The maximum time to detect the loss of communication from a peripheral device is
500ms.
Table D Timing specifications contained in DPI and SCANport
The Minimum Update Time (MUT), is based on the message type only. A standard
command and Datalink command could be transmitted from the same peripheral
faster than the MUT and still be O.K. Two successive Datalink commands or
standard commands will still have to be separated by the MUT, however.
DPI Host status messages only go out to peripherals once they log in and at least every 125ms
(to all attached peripherals). Peripherals time out if >250ms. Actual time is dependent on
number of peripherals attached. Minimum time goal is 5ms (may have to be dependent on
Port Baud Rate). DPI allows minimum 5ms status at 125k and 1ms status at 500k.
SCANport Host status messages only go out to peripherals once they log in. Peripherals time out if
>500ms. If Peripheral receives incorrect status message type, Peripheral generates an
error. Actual time is dependent on number of peripherals attached. SCANport allows
minimum rate of 5ms.
DPI Host determines MUT based on number of attached peripherals. Range of values from 2
to 125ms. Minimum goal time is 5ms. DPI allows 2ms min at 500k and 5ms min at 125k.
SCANport No MUT.
DPI
Peripheral command messages (including Datalinks) are generated on change-of-state,
but not faster than Host MUT and at least every 250ms. Host will time out if >500ms.
SCANport Command messages are produced as a result of Host status message. If no command
response to Host status within 3 status scan times, Host will time out on that peripheral.
DPI Peer message requests cannot be sent any faster than 2x of MUT.
SCANport No Peer message support
DPI
Host must ping every port at least one every 2 sec. Peripherals time out if >3 sec. Host will
wait maximum of 10ms (125k) or 5ms (500k) for peripheral response to ping. Peripherals
typical response time is 1ms. Peripherals only allow one pending explicit message (e.g.
ping response or peer request) at a time.
SCANport Host waits at least 10ms for response to ping. Host cannot send more than 2 event
messages (including ping) to a peripheral within 5ms. Peripherals typical response time is
1ms.
DPI Response to an explicit request or fragment must occur within 1 sec or device will time out
(applies to Host or Peripheral). Time-out implies retry from beginning. Maximum number
of fragments per transaction is 16. Flash memory is exception with 22 fragments allowed.
SCANport Assume same 1 sec time-out. Maximum number of fragments is 16
DPI
During Flash mode, host stops ping, but still supports status/command messages at a 1 –
5 sec rate. Drive will use 1 sec rate. Data transfer occurs via explicit message as fast as
possible (e.g. peripheral request, host response, peripheral request, etc.) but only
between two devices.
SCANport No Flash mode support