Rainbow Electronics ATmega64M1 - Manual (Page 173)

173
8209A–AVR–08/09
ATmega16M1/32M1/64M1
20.5.3 Baud Rate
With no baud rate prescaler (BRP[5..0]=0) the sampling point comes one time quantum too
early. This leads to a fail according the ISO16845 Test plan. It is necessary to lengthen the
Phase Segment 1 by one time quantum and to shorten the Phase Segment 2 by one time quan-
tum to compensate.
The baud rate selection is made by T
bit
calculation:
Tbit (1) = Tsyns + Tprs + Tphs1 + Tphs2
1. Tsyns = 1 x Tscl = (BRP[5..0]+ 1)/clk
IO
(= 1TQ)
2. Tprs = (1 to 8) x Tscl = (PRS[2..0]+ 1) x Tscl
3. Tphs1 = (1 to 8) x Tscl = (PHS1[2..0]+ 1) x Tscl
4. Tphs2 = (1 to 8) x Tscl = (PHS2[2..0] (2) + 1) x Tscl
5. Tsjw = (1 to 4) x Tscl = (SJW[1..0]+ 1) x Tscl
Notes: 1. The total number of Tscl (Time Quanta) in a bit time must be from 8 to 25.
2. PHS2[2..0] 2 is programmable to be
≤
PHS1[2..0] and 1.
20.5.4 Fault Confinement
(c.f. Section 20.8 “Error Management” on page 178 ).
20.5.5 Overload Frame
An overload frame is sent by setting an overload request (OVRQ). After the next reception, the
CAN channel sends an overload frame in accordance with the CAN specification. A status or
flag is set (OVRF) as long as the overload frame is sent.
Figure 20-9. Overload Frame
Ident "A" Cmd Message Data "A" CRC Interframe A Ident "B"
Overload Frame
Overload Frame RXCDAN
Setting OVRQ bit
OVFG bit
Resetting OVRQ bit
TXCDAN
OVRQ bit
Instructions