AT90CAN32 Automotive Atmel Corporation, AT90CAN32 Automotive Datasheet - Page 209

• Manufacturer Part Number: AT90CAN32 Automotive
• Manufacturer: Atmel Corporation

Specifications of AT90CAN32 Automotive

• Flash (kbytes): 32 Kbytes
• Pin Count: 64
• Max. Operating Frequency: 16 MHz
• Cpu: 8-bit AVR
• # Of Touch Channels: 16
• Hardware Qtouch Acquisition: No
• Max I/o Pins: 53
• Ext Interrupts: 8
• Usb Speed: No
• Usb Interface: No
• Spi: 1
• Twi (i2c): 1
• Uart: 2
• Can: 1
• Graphic Lcd: No
• Video Decoder: No
• Camera Interface: No
• Adc Channels: 8
• Adc Resolution (bits): 10
• Adc Speed (ksps): 15
• Analog Comparators: 1
• Resistive Touch Screen: No
• Temp. Sensor: No
• Crypto Engine: No
• Sram (kbytes): 2
• Eeprom (bytes): 1024
• Self Program Memory: YES
• Dram Memory: No
• Nand Interface: No
• Picopower: No
• Temp. Range (deg C): -40 to 125
• I/o Supply Class: 2.7 to 5.5
• Operating Voltage (vcc): 2.7 to 5.5
• Fpu: No
• Mpu / Mmu: no / no
• Timers: 4
• Output Compare Channels: 8
• Input Capture Channels: 2
• Pwm Channels: 7
• 32khz Rtc: Yes
• Calibrated Rc Oscillator: Yes

18.5.1
18.5.2
7682C–AUTO–04/08
SCL and SDA Pins
Bit Rate Generator Unit
Figure 18-9. Overview of the TWI Module
These pins interface the AVR TWI with the rest of the MCU system. The output drivers contain a
slew-rate limiter in order to conform to the TWI specification. The input stages contain a spike
suppression unit removing spikes shorter than 50 ns. Note that the internal pullups in the AVR
pads can be enabled by setting the PORT bits corresponding to the SCL and SDA pins, as
explained in the I/O Port section. The internal pull-ups can in some systems eliminate the need
for external ones.
This unit controls the period of SCL when operating in a Master mode. The SCL period is con-
trolled by settings in the TWI Bit Rate Register (TWBR) and the Prescaler bits in the TWI Status
Register (TWSR). Slave operation does not depend on Bit Rate or Prescaler settings, but the
CPU clock frequency in the slave must be at least 16 times higher than the SCL frequency. Note
that slaves may prolong the SCL low period, thereby reducing the average TWI bus clock
period. The SCL frequency is generated according to the following equation:
Note:
• TWBR = Value of the TWI Bit Rate Register
• TWPS = Value of the prescaler bits in the TWI Status Register
TWBR should be 10 or higher if the TWI operates in Master mode. If TWBR is lower than 10, the
master may produce an incorrect output on SDA and SCL for the reminder of the byte. The prob-
lem occurs when operating the TWI in Master mode, sending Start + SLA + R/W to a slave (a
slave does not need to be connected to the bus for the condition to happen).
Slew-rate
Address Match Unit
Control
Arbitration detection
START / STOP
Address Comparator
Address Register
SCL
Control
(TWAR)
Spike
Filter
Bus Interface Unit
SCL frequency
Spike Suppression
Address/Data Shift
Register (TWDR)
Slew-rate
Control
=
---------------------------------------------------------- -
16
SDA
Status Register
+
Ack
Spike
2(TWBR) 4
Filter
(TWSR)
CLKio
State Machine and
Control Unit
AT90CAN32/64/128
Status control
⋅
TWPS
Control Register
Bit Rate Generator
(TWCR)
Bit Rate Register
Prescaler
(TWBR)
TWI
Unit
209