KUNBUS-COM EtherCAT
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4.6 DPR - Dual Port RAM
-The COMS-Modul contains a special memory module (RAM with 1
Kbyte length), whose memory addresses the processor of the
module can also access, like an external processor, which is
connected to the module via the DPR interface.
If the application where the COMS-Modul is used should exchange
extensive data quickly, then this type of communication between the
base board and COMS-Modul is ideal. This absolutely requires the
use of a microprocessor on the base board, however, which operates
the DPR interface.
Many pins of the application interface are required for this parallel
access to the DPR. This results in a different PIN assignment in the
DPR mode of the module (this is switched on and off via the logic
level on PIN a14). In parallel access mode, no SSC or SDI interfaces
are available.
The data exchange between application circuitry and the COMS-
Modul via DPR can take place in two different ways:
– Process data is read in and read out cyclically from the Data Broker via
two fixed address ranges for input and output data. In this case, the
DPR reacts like another communication interface, as a producer and
consumer. The data is distributed according to the specifications set in
the Data Broker.
– Messages are exchanged via two address ranges for an input and
output "mailbox" by means of defined handshaking. The messages
include:
– Commands for writing and reading the memory registers
– Addresses of the memory registers
– Data lengths
– Register contents to be written or read
This communication via mailboxes replaces the Modbus
communication via SDI in parallel access mode (which is not
available in this mode). All parameters in parallel access mode can
only be read or written via CDI interface or DPR mailboxes.
To enable these two types of communication, the 1 Kbyte
memory of the DualPortRAM interface is subdivided into five
areas:
Dual Port RAM
Configuration
Incoming
mailbox
Outgoing
mailbox
Process data
input
Process data
output
Components
