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CHAPTER 13:
DOWNLOADABLE COMMUNICATION PROT0COLS
13.1 Overview
Through loadable protocol device drivers, certain models of the OCS family can provide the ability to
exchange data with remote devices such as variable-frequency drives, PLCs, and remote I/O
devices.
This feature greatly expands the OCS ’s control capability with negligible effect on the OCS ’s
ladder scan time.
Remote devices that communicate serially must do so under certain rules of data transfer known as a
protocol. Many device manufactures have created their own protocol for communications with their
device. For an OCS to communicate with a specific device, it must be loaded with the corresponding
serial communications protocol device driver that supports that protocol.
A limited number of protocol device drivers are packaged with the Cscape distribution; however, as
more are developed, they will be made available as add-on packages. A device driver is typically
distributed as a Windows module, which contains the Configuration Menus, Help Files and the Target
Executable Driver Code. When updating device drivers, an install routine loads the device driver to the
Cscape directory structure and makes that driver available to Cscape applications.
Once installed, the protocol device driver can be included as part of a Cscape application by selecting it
from a list of installed protocol device drivers and attaching it to the desired serial port (Program >
Protocol Config menu). Only one protocol device driver can be associated with a serial port, though
some OCS models support multiple protocols on a single Ethernet port.
Once the protocol is selected for a specific port, that port must be configured to match the bit transfer
size and rate of the target device(s). This is configured under the
Network Config
menu, which contains
port specific information such as the basic serial port parameters (i.e. baud rate, stop bits parity, retries,
etc.). In addition to the serial port parameters, this menu also contains the transaction scan update
control configuration and any network level protocol specific configuration.
Once the network is configured, each device on the serial communications network must be configured.
For some communications (i.e. RS232), the network can be limited to one device. The devices are
configured under the
Device Config
menu, which contains an arbitrary device name, the device ID and
optionally an OCS status register that contains any device fault information.
Once each device(s) is configured, a
Scan List
of entries must be created which defines the transfer of
data between a local (OCS) register(s) and a remote device register(s). These entries are created under
the
Data Mapping
menu, which contains an OCS register, a target device ID, a target device register
address, the number of registers to transfer, and update type.
Each entry can be configured for one of two types of initiating a transaction:
Polled and Triggered.
Polled type entries initiate a transaction with the remote device on every transaction scan. Triggered
type entries only initiate a transaction when a corresponding local (OCS) binary trigger register is
set
.
Once a triggered type transaction completes, the protocol device driver
resets
the local (OCS) binary
register to indicate completion. See Section 8.5 for more details on Polled and Triggered entries.
