Rainbow-electronics ATmega64M1 Manuel d'utilisateur télécharger pdf (Page 189)

189

8209A–AVR–08/09

ATmega16M1/32M1/64M1

• Bit 6:1 – BRP[5:0]: Baud Rate Prescaler

The period of the CAN controller system clock Tscl is programmable and determines the individ-

ual bit timing.

If ‘BRP[5..0]=0’, see Section 20.5.3 “Baud Rate” on page 173 and Section • “Bit 0 – SMP: Sam-

ple Point(s)” on page 190.

• Bit 0 – Res: Reserved

This bit is reserved for future use. For compatibility with future devices, it must be written to zero

when CANBT1 is written.

20.10.9 CANBT2 – CAN Bit Timing Register 2

• Bit 7– Res: Reserved

This bit is reserved for future use. For compatibility with future devices, it must be written to zero

when CANBT2 is written.

• Bit 6:5 – SJW[1:0]: Re-Synchronization Jump Width

To compensate for phase shifts between clock oscillators of different bus controllers, the control-

ler must re-synchronize on any relevant signal edge of the current transmission.

The synchronization jump width defines the maximum number of clock cycles. A bit period may

be shortened or lengthened by a re-synchronization.

• Bit 4 – Res: Reserved

This bit is reserved for future use. For compatibility with future devices, it must be written to zero

when CANBT2 is written.

• Bit 3:1 – PRS[2:0]: Propagation Time Segment

This part of the bit time is used to compensate for the physical delay times within the network. It

is twice the sum of the signal propagation time on the bus line, the input comparator delay and

the output driver delay.

• Bit 0 – Res: Reserved

This bit is reserved for future use. For compatibility with future devices, it must be written to zero

when CANBT2 is written.

Tscl =

BRP[5:0] + 1

clk

frequency

Bit 76543210

- SJW1 SJW0 - PRS2 PRS1 PRS0 - CANBT2

Read/Write - R/W R/W - R/W R/W R/W -

Initial Value - 0 0 - 0 0 0 -

Tsjw = Tscl x (SJW [1:0] +1)

Tprs = Tscl x (PRS [2:0] + 1)

1 2 ... 184 185 186 187 188 189 190 191 192 193 194 ... 342 343

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Rainbow-electronics ATmega64M1 Manuel d'utilisateur Page 189