MCP2510-EP Microchip Technology, MCP2510-EP Datasheet - Page 8

• Manufacturer Part Number: MCP2510-EP
• Description: Stand-Alone CAN Controller with SPI Interface
• Manufacturer: Microchip Technology

MCP2510
2.4
An Error Frame is generated by any node that detects
a bus error. An error frame, shown in Figure 2-4, con-
sists of two fields, an error flag field followed by an error
delimiter field. There are two types of error flag fields.
Which type of error flag field is sent depends upon the
error status of the node that detects and generates the
error flag field.
If an error-active node detects a bus error then the
node interrupts transmission of the current message by
generating an active error flag. The active error flag is
composed of six consecutive dominant bits. This bit
sequence actively violates the bit stuffing rule. All other
stations recognize the resulting bit stuffing error and in
turn generate error frames themselves, called error
echo flags. The error flag field, therefore, consists of
between six and twelve consecutive dominant bits
(generated by one or more nodes). The error delimiter
field completes the error frame. After completion of the
error frame, bus activity returns to normal and the inter-
rupted node attempts to resend the aborted message.
If an error-passive node detects a bus error then the
node transmits an error-passive flag followed by the
error delimiter field. The error-passive flag consists of
six consecutive recessive bits, and the error frame for
an error-passive node consists of 14 recessive bits.
From this, it follows that unless the bus error is detected
by the node that is actually transmitting, the transmis-
sion of an error frame by an error-passive node will not
affect any other node on the network. If the transmitting
node generates an error-passive flag then this will
cause other nodes to generate error frames due to the
resulting bit stuffing violation. After transmission of an
error frame, an error-passive node must wait for six
consecutive recessive bits on the bus before attempt-
ing to rejoin bus communications.
The error delimiter consists of eight recessive bits and
allows the bus nodes to restart bus communications
cleanly after an error has occurred.
DS21291C-page 8
Error Frame
Preliminary
2.5
An Overload Frame, shown in Figure 2-5, has the same
format as an active error frame. An overload frame,
however can only be generated during an lnterframe
space. In this way an overload frame can be differenti-
ated from an error frame (an error frame is sent during
the transmission of a message). The overload frame
consists of two fields, an overload flag followed by an
overload delimiter. The overload flag consists of six
dominant bits followed by overload flags generated by
other nodes (and, as for an active error flag, giving a
maximum of twelve dominant bits). The overload delim-
iter consists of eight recessive bits. An overload frame
can be generated by a node as a result of two condi-
tions. First, the node detects a dominant bit during the
interframe space which is an illegal condition. Second,
due to internal conditions the node is not yet able to
start reception of the next message. A node may gen-
erate a maximum of two sequential overload frames to
delay the start of the next message.
2.6
The lnterframe Space separates a preceeding frame
(of any type) from a subsequent data or remote frame.
The interframe space is composed of at least three
recessive bits called the Intermission. This is provided
to allow nodes time for internal processing before the
start of the next message frame. After the intermission,
the bus line remains in the recessive state (bus idle)
until the next transmission starts.
Overload Frame
Interframe Space
1999 Microchip Technology Inc.