IzoT U60 DIN Network Interface User’s Guide
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U60 when the driver is opened by an application. The OpenLDV driver for Windows
includes a U60 driver, starting with OpenLDV 5.
Protocol Processing Selection
The U60 has two protocol processing modes of operation,
Layer 5 mode
and
Layer 2
mode
.
•
In
Layer 5 mode
, Layers 1 to 5 of the ISO/IEC 14908-1 and 14908-2 protocol
stack are handled by the U60, and Layer 5 messages are exchanged between
the U60 and the host using the U60 LLP. Layer 5 mode requires less code on
the host than Layer 2 mode since Layer 5 mode leverages the ISO/IEC 14908-
1 Layers 3 through 5 protocol stack implemented by the Neuron firmware.
The U60 Layer 5 driver interface to the host application is compatible with
the MIP/P20 and MIP/P50 driver interface to the host application. The driver
communicates with the U60 using the link-layer protocol (LLP), and the U60
LLP is different from the MIP/P20 and MIP/P50 LLP. The U60 LLP is
described in this section.
•
In
Layer 2 mode
, Layers 1 and 2 of the ISO/IEC 14908-1 and 14908-2 protocol
stack are handled by the U60, and Layer 2 messages are exchanged between
the U60 and the host using the LLP. The host must implement Layers 3
through 7 when the U60 is running in Layer 2 mode. You can use Layer 2
mode with the Echelon LonTalk Device Stack EX running on the host to
create high performance controllers that support more address table entries
and simultaneous transactions than can be supported by the U60 with a
Layer 5 interface. The LonTalk Device Stack EX includes a complete
implementation of ISO/IEC 14908-1 Layers 3 through 5 that runs on a host
and interfaces with a native LON interface such as the U60 module, or
interfaces directly with an Ethernet or Wi-Fi interface on the host.
If you are using the OpenLDV 5 driver for Windows or newer, your application can
select the protocol processing mode of operation by opening the driver with the
ldv_open_cap()
function and specifying the mode with the
nDeviceCaps
parameter. Set
nDeviceCaps
to
LDV_DEVCAP_L2
for Layer 2 mode or
LDV_DEVCAP_L5
for Layer 5 mode.
If you are using the U60 driver for Linux, you need to specify the protocol processing
mode in the driver source code, and rebuild the driver for your Linux platform. The
protocol processing mode is selected in the call to
U50LinkStart()
in the
u50_dev_open()
function. Specify the mode in the last parameter in the call to
U50LinkStart()
. Specify
U50_OPEN_LAYER2
for Layer 2 mode or
U50_OPEN_LAYER5
for Layer 5 mode.
Link Layer Protocol (LLP)
The U60 communicates with a host over a USB connection using the U60 link-layer
protocol (LLP). The driver manages the host end of the U60 LLP, and initializes the
U60 when the driver is opened by an application.
The basic component of the U60 LLP is the code packet, which starts with an 0x7E
escape code. If an escape code appears in a normal data stream it is followed by
another escape code and interpreted as a single data byte value rather than the start
of the code packet. The following figure illustrates the code packet layout.
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