16.5.4 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 formatted 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 16-14 on page 155).
16.5.5 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 message 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, ...
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
clk
8
CANTCON
ENFG
IO
clk
CANTIM
TTC SYNCTTC
overrun
OVRTIM
CANTIM
TXOK[i]
RXOK[i]
"EOF"
"SOF"
CANSTM[i]
CANTTC
16.6.1 Prescaler
An 8-bit prescaler is initialized by CANTCON register. It receives the clkIO frequency divided by 8. It provides clkCANTIM
frequency to the CAN timer if the CAN controller is enabled.
TclkCANTIM = TclkIO 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.
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ATmega16/32/64/M1/C1 [DATASHEET]
7647O–AVR–01/15
MICROCHIP [ MICROCHIP ]
