atmega32u4-16mu ATMEL Corporation, atmega32u4-16mu Datasheet - Page 248

• Manufacturer Part Number: atmega32u4-16mu
• Description: Atmega32u4 8-bit Avr Microcontroller With 32k Bytes Of Isp Flash And Usb Controller
• Manufacturer: ATMEL Corporation

21.5.1
21.5.2
248
ATmega32U4
SCL and SDA Pins
Bit Rate Generator Unit
Figure 21-9. 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 pull-ups 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:
Address Match Unit
Slew-rate
Arbitration detection
Control
START / STOP
Address Comparator
Address Register
Control
SCL
(TWAR)
Spike
Filter
Bus Interface Unit
Spike Suppression
Address/Data Shift
Register (TWDR)
Slew-rate
Control
SDA
Status Register
Ack
Spike
Filter
(TWSR)
State Machine and
Control Unit
Status control
Bit Rate Generator
Control Register
Bit Rate Register
Prescaler
(TWCR)
(TWBR)
7766A–AVR–03/08