ST72521 datasheet(136/211 Pages) STMICROELECTRONICS

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ST72521

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CONTROLLER AREA NETWORK (Cont’d)

CONTROL/STATUS REGISTER (CSR)

Read/Write

Reset Value: 00h

Bit 6 = BOFF

Bus-Off State

− Read Only

Set by hardware to indicate that the node is in bus-

off state, i.e. the Transmit Error Counter exceeds

255.

Reset by hardware to indicate that the node is in-

volved in bus activities.

Bit 5 = EPSV

Error Passive State

− Read Only

Set by hardware to indicate that the node is error

passive.

Reset by hardware to indicate that the node is either

error active (BOFF = 0) or bus-off.

Bit 4 = SRTE

Simultaneous Receive/Transmit En-

able

− Read/Set/Clear

Set by software to enable simultaneous transmis-

sion and reception of a message passing the ac-

ceptance filtering. Allows to check the integrity of

the communication path.

Reset by software to discard all messages trans-

mitted by the node. Allows remote and data frames

to share the same identifier.

Bit 3 = NRTX

No Retransmission

− Read/Set/Clear

Set by software to disable the retransmission of un-

successful messages.

Cleared by software to enable retransmission of

messages until success is met.

Bit 2 = FSYN

Fast Synchronization

− Read/Set/Clear

Set by software to enable a fast resynchronization

when leaving standby mode, i.e. wait for only 11 re-

cessive bits in a row.

Cleared by software to enable the standard resyn-

chronization when leaving standby mode, i.e. wait

for 128 sequences of 11 recessive bits.

Bit 1 = WKPS

Wake-up Pulse

− Read/Set/Clear

Set by software to generate a dominant pulse when

leaving standby mode.

Cleared by software for no dominant wake-up

pulse.

Bit 0 = RUN

CAN Enable

− Read/Set/Clear

Set by software to leave standby mode after 128 se-

quences of 11 recessive bits or just 11 recessive

bits if FSYN is set.

Cleared by software to request a switch to the

standby or low-power mode as soon as any on-go-

ing transfer is complete. Read-back as 1 in the

meantime to enable proper signalling of the standby

state. The CPU clock may therefore be safely

switched OFF whenever RUN is read as 0.

BOFF

EPSV

SRTE

NRTX

FSYN WKPS

RUN

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