Rainbow-electronics ATmega64C1 Manual do Utilizador descarregar pdf (Página 180)

180

7647A–AVR–02/08

ATmega32/64/M1/C1

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,

...

16.6 CAN Timer

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

(TTC).

Figure 16-11. CAN Timer Block Diagram

16.6.1 Prescaler

An 8-bit prescaler is initialized by CANTCON register. It receives the clk

frequency divided by

8. It provides clk

CANTIM

frequency to the CAN Timer if the CAN controller is enabled.

Tclk

CANTIM

= Tclk

x 8 x (CANTCON [7:0] + 1)

16.6.2 16-bit Timer

This timer starts counting from 0x0000 when the CAN controller is enabled (ENFG bit). When

the timer rolls over from 0xFFFF to 0x0000, an interrupt is generated (OVRTIM).

16.6.3 Time Triggering

Two synchronization modes are implemented for TTC (TTC bit):

– synchronization on Start of Frame (SYNCTTC=0),

– synchronization on End of Frame (SYNCTTC=1).

In TTC mode, a frame is sent once, even if an error occurs.

16.6.4 Stamping Message

The capture of the timer value is done in the MOb which receives or sends the frame. All man-

aged MOb are stamped, the stamping of a received (sent) frame occurs on RxOk (TXOK).

clk

CANTIM

CANTTCCANSTM[i]

CANTCON

TTC SYNCTTC

"EOF

"SOF

OVRTIM

TXOK[i]

RXOK[i]

overrun

ENFG

1 2 ... 175 176 177 178 179 180 181 182 183 184 185 ... 365 366

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