MCP25020ISLASHP datasheet(27/66 Pages) MICROCHIP

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DS21664D-page 27

MCP2502X/5X

4.5

Automatic Transmission

The MCP2502X/5X can automatically initiate four

different message types to indicate the following

situations:

• Edge detected on a digital input (TXID2).

• Threshold exceeded on an analog input (TXID2).

• Error condition (Read Error output message).

• Scheduled transmissions (TXID0).

The buffers have an implied transmit priority, where

buffer 2 is the highest and buffer 0 is the lowest.

Therefore, multiple message buffers can be requested

for transmission and each one will be sent in order of

priority.

4.5.1

DIGITAL INPUT EDGE DETECTION

Each GPIO pin configured as a digital input can be

individually configured to automatically transmit a

message when a defined edge occurs, as explained in

the GPIO module section. When transmitting this

message, the MCP2502X/5X uses TXID2. The DLC is

set to two and the first two bytes of the Read A/D

registers (IOINTFL and GPIO) are sent.

4.5.2

ANALOG INPUT THRESHOLD

DETECTION

Each GPIO pin that has been configured as an analog

input can be individually configured to automatically

transmit a message when a threshold is exceeded as

described in the Analog-to-Digital Converter Module

section. The MCP2502X/5X sends TXID2 when

transmitting this message. The DLC is set to eight and

the eight bytes of the ‘Read A/D Registers’ are sent.

4.5.2.1

Hysteresis Function

This function is automatic and will insure that an analog

value that is on the compare edge (i.e., toggling LSb)

does not fill the CAN bus with continuous A/D message

transmissions.

The hysteresis uses the two LSb’s of the compare

configurable by the user. They will be forced to either

b’00’

or b’11’, depending on the compare polarity. If

configured for A/D result > compare register, the

automatic transmission will occur when the A/D value

is greater than or equal to b’nnnn nnnn 11’ and

reset when less than or equal to b’nnnn nnnn 00’.

The opposite conditions must occur if the compare

polarity is set for A/D result < compare register.

A hysteresis example:

• The user sets the upper-eight bits of the 10-bit

compare register (ADCMP0H). The lower-two bits

of the compare register are not configurable by

the user and are forced to either b’11’ or b’00’

depending on the polarity of the compare

threshold (i.e., transmit is triggered above or

below the compare value via the IOINTPO

• The user sets the polarity of the compare

threshold (IOINTPO). In this example, the

threshold is set for triggering a message on an

A/D > compare register. The two LSb’s are forced

to b’11’.

• When the A/D conversion exceeds the compare

transmission will occur once.

• In order for the automatic transmission to occur

again, the A/D value must first drop below the

compare register b’nnnn nnnn 00’ and then

back above the compare register

b’nnnn nnnn 11’

FIGURE 4-1:

HYSTERESIS

FUNCTION

4.5.3

ERROR CONDITION

The MCP2502X/5X can be configured to automatically

transmit a message whenever one or more of the

following error conditions occur:

• Receiver has entered error-warning state

• Receiver has entered error-passive state

• Transmitter has entered error-warning state

• Transmitter has entered error-passive state

• A Receive buffer has overflowed

Note:

The GPIO register that is sent with the

message (data byte 2) can be ignored if

there are no digital inputs enabled for

change-of-state, as it contains no useful

information for the Analog Input Threshold

Detect function.

LSbs = b’11’

Set to Trigger when A/D>Compare Register

LSbs = b’00’

LSbs = b’11’

LSbs = b’00’

Set to Trigger when A/D<Compare Register

A/D above compare,

Message sent

A/D above compare,

Message sent

A/D below compare,

Reset

A/D below compare,

Message sent

A/D below compare,

Message sent

A/D above compare,

Reset

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