ATTINY861A-SU Atmel, ATTINY861A-SU Datasheet - Page 124

• Manufacturer Part Number: ATTINY861A-SU
• Description: IC, MCU, 8BIT, 8K FLASH, 20SOIC
• Manufacturer: Atmel

Specifications of ATTINY861A-SU

• Controller Family/series: ATtiny
• No. Of I/o's: 16
• Eeprom Memory Size: 512Byte
• Ram Memory Size: 512Byte
• Cpu Speed: 20MHz
• No.: RoHS Compliant
• Core Size: 8bit
• Program Memory Size: 8KB
• Oscillator Type: External, Internal
• Rohs Compliant: Yes

13.3
13.3.1
124
Functional Descriptions
ATtiny261A/461A/861A
Three-wire Mode
The 4-bit counter can be both read and written via the data bus, and it can generate an overflow
interrupt. The data register and the counter are clocked simultaneously by the same clock
source, allowing the counter to count the number of bits received or transmitted and generate an
interrupt when the transfer is complete. Note that when an external clock source is selected the
counter counts both clock edges. In this case the counter counts the number of edges, and not
the number of bits. The clock can be selected from three different sources: The USCK pin, the
Timer/Counter0 Compare Match or from software.
The Two-wire clock control unit can generate an interrupt when a start condition is detected on
the Two-wire bus. It can also generate wait states by holding the clock pin low after a start con-
dition is detected, or after the counter overflows.
The USI Three-wire mode is compliant to the Serial Peripheral Interface (SPI) mode 0 and 1, but
does not have the slave select (SS) pin functionality. However, this feature can be implemented
in software if necessary. Pin names used by this mode are: DI, DO, and USCK.
Figure 13-2. Three-wire Mode Operation, Simplified Diagram
Figure 13-2
The two USI Data Register are interconnected in such way that after eight USCK clocks, the
data in each register are interchanged. The same clock also increments the USI’s 4-bit counter.
The Counter Overflow (interrupt) Flag, or USIOIF, can therefore be used to determine when a
transfer is completed. The clock is generated by the Master device software by toggling the
USCK pin via the PORT Register or by writing a one to the USITC bit in USICR.
SLAVE
MASTER
Bit7
Bit7
shows two USI units operating in three-wire mode, one as Master and one as Slave.
Bit6
Bit6
Bit5
Bit5
Bit4
Bit4
Bit3
Bit3
Bit2
Bit2
Bit1
Bit1
Bit0
Bit0
PORTxn
USCK
USCK
DO
DO
DI
DI
8197B–AVR–01/10