Rainbow-electronics ATmega64M1 Manuel d'utilisateur télécharger pdf (Page 177)

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8209A–AVR–08/09

ATmega16M1/32M1/64M1

20.6.4 MOb Page

Every MOb is mapped into a page to save place. The page number is the MOb number. This

page number is set in CANPAGE register. The other numbers are reserved for factory tests.

CANHPMOB register gives the MOb having the highest priority in CANSIT registers. It is format-

ted to provide a direct entry for CANPAGE register. Because CANHPMOB codes CANSIT

registers, it will be only updated if the corresponding enable bits (ENRX, ENTX, ENERR) are

enabled (c.f. Figure 20-14).

20.6.5 CAN Data Buffers

To preserve register allocation, the CAN data buffer is seen such as a FIFO (with address

pointer accessible) into a MOb selection.This also allows to reduce the risks of un-controlled

accesses.

There is one FIFO per MOb. This FIFO is accessed into a MOb page thanks to the CAN mes-

sage register.

The data index (INDX) is the address pointer to the required data byte. The data byte can be

read or write. The data index is automatically incremented after every access if the AINC* bit is

reset. A roll-over is implemented, after data index=7 it is data index=0.

The first byte of a CAN frame is stored at the data index=0, the second one at the data index=1,

...

20.7 CAN Timer

A programmable 16-bit timer is used for message stamping and time trigger communication

(TTC).

Figure 20-11. CAN Timer Block Diagram

clk

CANTIM

CANTTCCANSTM[i]

CANTCON

TTC SYNCTTC

"EOF

"SOF

OVRTIM

TXOK[i]

RXOK[i]

overrun

ENFG

1 2 ... 172 173 174 175 176 177 178 179 180 181 182 ... 342 343

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Rainbow-electronics ATmega64M1 Manuel d'utilisateur Page 177