MCP25025-E/SL Microchip Technology, MCP25025-E/SL Datasheet - Page 11
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MCP25025-E/SL
Manufacturer Part Number
MCP25025-E/SL
Description
CAN I/O Expander Family, -40C to +125C, 14-SOIC 150mil, TUBE
Manufacturer
Microchip Technology
Datasheet
1.MCP25025-ESL.pdf
(66 pages)
2.5
This part of the CAN module supports the transmitting,
receiving and acceptance of CAN messages.
Three transmit buffers are used for the three transmit
message IDs, as discussed later in this section. Two
receive buffers store the CAN message’s arbitration
field, control field and the data field.
One mask defines which bits are to be applied to either
filter. The mask can be regarded as defining “don’t
care” bits for the filter.
Each of the two filters define a bit pattern that will be
compared to all incoming messages. All filter bits that
have not been defined as “don’t care” by the mask are
applied to the message.
2.5.1
The MCP2502X/5X device contains three separate
transmit message ID’s: TXID0, TXID1 and TXID2. The
data length code is predefined for each of the various
output messages, with the data that is transmitted
coming directly from the contents of the device’s
peripheral registers.
2.5.1.1
TXID0 contains the identifier that is used when trans-
mitting
(STCON.STEN = 1), the On Bus message will be
transmitted at predefined intervals. Depending on the
message-select bit (STCON.STMS = 1), the CAN
message will send GPIO and A/D data.
Transmit Message ID0 will not automatically be sent
when the device is brought out of sleep.
2.5.1.2
TXID1 contains the identifier that is used when the
MCP2502X/5X sends the Command Acknowledge
message, the Receive Overflow message and/or the
Error Condition message. All message types use the
same identifier.
The CAEN bit, in the OPTREG2 register, selects
between the Command Acknowledge and Receive
Overflow operation. These message types have a DLC
of 0 and do not contain any data. The Error Condition
message can occur anytime, has a DLC of 3 and
contains the EFLG, TEC and REC data values.
© 2007 Microchip Technology Inc.
Note:
Buffers, Masks, and Filters
the
A zero data length On Bus message will be
transmitted
regardless of scheduled transmission-
enable status.
TRANSMIT MESSAGE ID’S
Transmit Message ID0 (TXID0)
Transmit Message ID1 (TXID1)
On
Bus
once
message.
after
If
power-up,
enabled
Command Acknowledge: TXID1 sends a Command
Acknowledge message when the MCP2502X/5X
receives an Input Message and processes the
instruction (and OPTREG2.CAEN = 1). This message
is used as a hand shake for the node requesting the
modification of the MCP2502X/5X. There is no data
associated with this message.
Receive Overflow: TXID1 sends a Receive Overflow
message if there is a Receive Overflow condition (and
OPTREG2.CAEN = 0). This only occurs if the device
has received a valid message before processing the
previous valid message from the same receive buffer.
There is no data associated with this message.
Error Condition: An Error Condition message is
transmitted if the TEC or REC counters reach error
warning (> 95) or error passive (> 127). This message
contains the TXID1 identifier and the TEC, REC and
EFLG counters.
A hysteresis is implemented in hardware that prevents
messages from repeatedly being transmitted due to
error counts changing by one or two bits. Once a
message is sent for an error warning (TEC or REC >
95), the message will not trigger again until the error
counter ≤ 79 and back to > 95 (hysteresis = 17 counts).
Similarly, an error passive message is sent at TEC or
REC > 127 and is not sent again until the error counter
≤ 111 and back to >127 (hysteresis = 17 counts).
2.5.1.3
Transmit ID2 contains the identifier that is used when
transmitting
including digital input edge detection and/or analog
input exceeding a threshold. This message will also be
sent when the device wakes up from sleep due to a
digital input change-of-state condition (i.e., change-of-
state occurs on input configured to transmit on
change-of-state).
2.6
The MCP2505X contains two receive buffers, each
with their own filter. There is also a Message Assembly
Buffer (MAB) that acts as a third receive buffer (see
Figure 2-1).
The two receive buffers, combined with the MAB help,
insure that received messages will be processed while
minimizing the chances of receive buffer overrun due to
maximum bus loading of messages destined for the
MCP2502X/5X.
Note:
Receive Buffers
The receive buffers are used by the
MCP2502X/5X to implement the command
messages
accessible.
Transmit Message ID2 (TXID2)
auto-conversion-initiated
MCP2502X/5X
and
are
DS21664D-page 11
not
messages,
externally