Rockwell Automation 1756-DMF30 ControlLogix Drive Module - Manual (Page 32)

Publication 1756-UM522B-EN-P - February 2003
3-6 Drive Module Features
The following requirements apply to communication format choices:
•
If a Drive module does not receive data (e.g. the first node in a
daisy chain topology), you must choose the
No Receive Data
Receive Port communication format.
•
If a Drive module does not transmit data (e.g. an end node), you
must choose the
No Transmit Data Transmit Port
communications format.
•
The receive communication format for any Drive module that
receives data must match the transmit communications format of
the upstream node in the system.
Internal Scan on Drive Module
Every 500
µ
S, the Drive module scans its internal hardware and
captures a “snapshot” of the data there. This data is then sent to the
local owner-controller at the Change of State (COS) instance,
independent of the requested packet interval (RPI) rate. But,
depending on the communications formats chosen during module
configuration, data types are transmitted between SynchLink nodes
(via the fiber optic cable) at various rates and may be transmitted
multiple times between the 500
µ
S snapshots.
The Drive module updates its receive and transmit buffers once every
500
µ
S. Because direct data can be passed through from node to node
once every 50
µ
S, up to 10 nodes can be updated with direct data in a
single 500
µ
S SynchLink scan. Pass-through functionality only applies
IMPORTANT
The receive and transmit on the same module do not have
to match.
Also, once the module is created, the communications
format cannot be changed. The module must be deleted
and recreated.
IMPORTANT
The transfer rate times listed in Table 3.A and
Table 3.B only represent the rate at which data is
passed between SynchLink modules over the fiber
optic cable.
Although the data is passed over the fiber optic cable
at various rates, depending on the communications
format choices, the
owner-controllers in each local
chassis only receive the data after the local
SynchLink module’s internal scan every 500
µ
S .