AT91SAM7X128 Atmel, AT91SAM7X128 Datasheet - Page 513

• Manufacturer Part Number: AT91SAM7X128
• Description: MCU 32-Bit 91S ARM7TDMI RISC 128KB Flash 1.8V/3.3V 100-Pin LQFP
• Manufacturer: Atmel

Specifications of AT91SAM7X128

• Package: 100LQFP
• Device Core: ARM7TDMI
• Family Name: 91S
• Maximum Speed: 55 MHz
• Ram Size: 32 KB
• Program Memory Size: 128 KB
• Operating Supply Voltage: 1.8|3.3 V
• Data Bus Width: 32 Bit
• Program Memory Type: Flash
• Number Of Programmable I/os: 62
• Interface Type: CAN/Ethernet/SPI/I2S/TWI/USART/USB
• On-chip Adc: 8-chx10-bit
• Operating Temperature: -40 to 85 °C
• Number Of Timers: 3

Figure 36-5. CAN Bit Timing
6120H–ATARM–17-Feb-09
CAN Clock
MCK
SYNC_
t
CSC
SEG
The SAMPLE POINT is the point in time at which the bus level is read and interpreted as the
value of that respective bit. Its location is at the end of PHASE_SEG1.
The ReSynchronization Jump Width defines the limit to the amount of lengthening or shortening
of the Phase Segments.
SJW is programmable to be the minimum of PHASE SEG1 and 4 TQ.
If the SMP field in the CAN_BR register is set, then the incoming bit stream is sampled three
times with a period of half a CAN clock period, centered on sample point.
In the CAN controller, the length of a bit on the CAN bus is determined by the parameters (BRP,
PROPAG, PHASE1 and PHASE2).
The time quantum is calculated as follows:
Note: The BRP field must be within the range [1, 0x7F], i.e., BRP = 0 is not authorized.
To compensate for phase shifts between clock oscillators of different controllers on the bus, the
CAN controller must resynchronize on any relevant signal edge of the current transmission. The
resynchronization shortens or lengthens the bit time so that the position of the sample point is
shifted with regard to the detected edge. The resynchronization jump width (SJW) defines the
maximum of time by which a bit period may be shortened or lengthened by resynchronization.
Example of bit timing determination for CAN baudrate of 500 Kbit/s:
PROP_SEG
• SJW: ReSynchronization Jump Width.
t
PRS
MCK = 48MHz
CAN baudrate= 500kbit/s => bit time= 2us
t
t
BIT
CSC
t
t
t
PRS
PHS2
PHS1
t
SJW
=
=
=
t
CSC
=
=
(
=
BRP
t
CSC
NOMINAL BIT TIME
t
t
AT91SAM7X512/256/128 Preliminary
t
CSC
CSC
CSC
PHASE_SEG1
+
t
×
+
PRS
×
×
×
t
1
(
PHS1
PROPAG
)
(
(
(
PHASE2
SJW
PHASE1
⁄
+
t
MCK
PHS1
+
1
+
)
+
+
+
t
1
PHS2
1
1
)
)
)
Sample Point
PHASE_SEG2
t
PHS2
Transmission Point
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