Protocol analysis
R&S
®
RTE
878User Manual 1326.1032.02 ─ 20
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Support of two methods for frame transfer management, the event trigger method
and the polling method.
The event trigger method can be used when the focus is placed on the responsive-
ness of the slave node communication. The polling method puts the focus on the
communication periodicity.
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Maximum baud rate of 20kbit/s
●
Up to 16 nodes connected to a communication bus
Frame types
The CXPI protocol defines three types of frames:
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Normal frame: it varies in length according to the frame transfer method. The
PTYPE field is only used for the polling method.
The normal frame is used to transfer compact data.
Figure 13-113: CXPI normal frame
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Sleep frame: it has a fixed length and fixed values for the PID and data fields. It is
sent by the master node to command the slave nods to change into sleep state.
Figure 13-114: CXPI sleep frame
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Long frame: it varies in length according to the frame transfer method. The PTYPE
field is only used for the polling method.
The long frame is used to transfer large amount of data.
Figure 13-115: CXPI long frame
During measurements further type of frames may also occur: PTYPE only, PID only
and PTYPE + PID only.
Frame fields
The different frames may contain the following fields:
●
PID: consists of a frame identifier (7 bits) and one parity bit.
●
Protected TYPE (PTYPE): a special PID field with a frame identifier of 00 (hex)
and a parity of 1. It is used only in the polling method.
●
Frame information: it consists of the following fields:
– Data Length Code (DLC): 4 bits that indicate the length of the data byte of a
normal frame.
– Network Management (NM): 2 bits indicating if the frame is in wakeup or
sleep mode.
CXPI (option R&S
RTE-K76)
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