Admin at 16:47, 13 February 2013

2013-02-13T16:47:21Z

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== (**COPIED FROM ENGLISH PAGE**) ==The Universal Serial Interface (USI) is a multi purpose hardware resource which provide the basics hardware for various serial communications and is faster and reliable then implementing it in software.

You mainly find the USI on ATTINY devices but also for example on ATMEGA169.

 

USI Features:
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| Two-wire Synchronous Data Transfer
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• Three-wire Synchronous Data Transfer

• Data Received Interrupt

• Wakeup from Idle Mode

 

The USI can be used in Two wire mode and in three wire mode:
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| 2 wire mode --> I2C/TWI
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| 3 wire mode --> SPI
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The USI handle only the low level communication. High level communication for example for 2 wire mode (I2C) like address setting, message interpreting or preparing of data needs to be handled by software in the main loop.

There are Application Notes from Atmel available:

 

[http://www.atmel.com/Images/doc2560.pdf AVR312: Using the USI module as a I2C slave]

[http://www.atmel.com/Images/doc2561.pdf AVR310: Using the USI module as a I2C master]

 

The 3 wire mode (SPI) is easier to implement and therefore shown here as an example.

The Slave Select (SS) needs to be implemented in software if needed.

The USI Pin names are: DI, DO and USCK.

 

[http://www.atmel.com/Images/doc2582.pdf AVR319: Using the USI module for SPI communication]

 

 

 

= See also: =

[[Using_the_SPI_protocol|Using the SPI protocol]], [[SPISLAVE]], [[Using_the_I2C_protocol|Using I2C Protocol]], [[CONFIG_TWISLAVE|confiig TWISLAVE]], [[I2C_TWI_Slave|I2C TWI Slave]]

 

 

Following an example how to use an ATTINY as an SPI Master and another example show an SPI Slave over USI.

 

= Example (SPI Master with USI): =

 

1. Configure the port pin's:

 

'---------Using ATTINY as SPI MASTER over USI----------------------------------- Config Portb.2 = Output                                     'USCK ----> SCK (Slave) Config Portb.1 = Output                                     'DO   ----> SDI (Slave) Config Portb.0 = Input                                     'DI   ----> SDO (Slave) Set Portb.0 Sdo Alias Pinb.0                                           'Pullup

 

2. Configure the Slave Select

 

Config Portb.3 = Output                                     'Slave Select (SS) ----> SEL (Slave) Set Portb.3 Sel Alias Portb.3

 

3. Configure the 3 wire mode

 

Set Usicr.usiwm0                                           'Three-wire mode. Uses DO, DI, and USCK pins.   'The Data Output (DO) pin overrides the corresponding bit in the PORTA 'register. However, the corresponding DDRA bit still controls the data direction. 'When the port pin is set as input the pin pull-up is controlled by the PORTA bit. 'The Data Input (DI) and Serial Clock (USCK) pins do not affect the normal port 'operation. When operating as master, clock pulses are software generated by 'toggling the PORTA register, while the data direction is set to output. The 'USITC bit in the USICR Register can be used for this purpose.

 

4. Function for send or receive a byte over USI (SPI Master mode)

 

Const Usi_clk_low = &B0001_0001 Const Usi_clk_high = &B0001_0011   'Wirte or read a byte over USI in SPI Master Mode Function Usi_byte(usi_out As Byte) As Byte   Local I As Byte     Usidr = Usi_out                                       'Byte to write over USI       For I = 1 To 8          Usicr = Usi_clk_low                               'Toggle the USI Clock to send or receive the single bits over USI (8 Bit)          Usicr = Usi_clk_high       Next    Usi_byte = Usidr                                       'Byte received over USI End Function

 

5. call the function to send/receive a byte

 

Reset Sel   Usi_return = Usi_byte(my_byte) Set Sel

 

 

 

= Example (SPI Slave with USI): =

The following example show how to use an USI of ATTINY85 as SPI SLAVE.

(you will also find the SPI Master for this USI of ATTINY85 as SPI SLAVE example)

 

ATXMEGA (SPI Master) <-----SPI------> (SPI Slave over USI) ATTIN85

 

1. First we configure the USI in Three-wire Mode

2. Setup the USI Overflow Interrupt

3. And wait until the USI Oveflow Interrupt is fired

4. Then we read the USI Data-Register and clear the USI Interrupt flag

 

 

  ' Using USI as an SPI slave with Attiny85 ' The ATTINY85 work with 3.3 V so we can direct connect it to an ATXMEGA ' Following you find also a SPI configuration with an XMEGA as SPI Master which I have tested with this SPI Slave   '( Config Spid = Hard , Master = Yes , Mode = 0 , Clockdiv = Clk128 , Data_order = Msb , Ss = Auto 'SS = Auto set the Slave Select (SS) automatically before a print #X or input #X command  (including initialization of the pin) 'Master SPI clock = 32MHz/Clk128 = 250KHz Open "SPID" For Binary As #12 ')   $regfile = "ATtiny85.DAT"                                    $crystal = 8000000                                         'internal crystal $hwstack = 32                                                $swstack = 10                                                $framesize = 30   Dim B As Byte Dim Usi_data_ready As Bit   Config Portb.1 = Output                                     'DO   ---> MISO of ATXMEGA (PD6)   Config Portb.2 = Output                                     'USCK ---> SCK of ATXMEGA  (PD7) Set Portb.2                                                 'enable Pullup   Config Portb.0 = Input                                     'DI   ---> MOSI of ATXMEGA (PD5) Set Portb.0                                                 'enable Pullup   'We do not use Slave Select in this example but this would be the configuration Config Portb.4 = Input                                     'Slave Select Set Portb.4                                                 ' enable Pullup Ss Alias Pinb.4     Config Portb.3 = Output                                     'Serial Debug output Open "comb.3:9600,8,n,1" For Output As #1 Print #1 , "serial output"   'Init USI as SPI Slave in USICR = USI Control Register Set Usicr.usiwm0                                           'Three-wire mode. Uses DO, DI, and USCK pins. Set Usicr.usics1                                           'Clock Source: External, positive edge ; External, both edges Set Usicr.usioie                                           'USI Counter Overflow Interrupt Enable     On Usi_ovf Usi_overflow_int Enable Usi_ovf Enable Interrupts     Do If Usi_data_ready = 1 Then     Reset Usi_data_ready     Print #1 , B                                         'print the received byte over debug output End If Loop   End                                                         'end program     ' After eight clock pulses (i.e., 16 clock edges) the 4-Bit USI counter will generate an overflow interrupt ' A USI Overflow Int can also wakeup the Attiny from Idle mode if needed Usi_overflow_int:     Set Usi_data_ready     B = Usidr     Usisr = &B01_000000                                   'Reset Overflow Flag and reset 4-Bit USI counter Return

 

 

 

= SPI Master for the ATTIN85 as SPI Slave over USI: =

 

    'This is the SPI MASTER for the ATTINY85 with USI in SPI Slave Mode   $regfile = "xm256a3bdef.dat" $crystal = 32000000                                         '32MHz $hwstack = 64 $swstack = 40 $framesize = 80     Config Osc = Disabled , 32mhzosc = Enabled Config Sysclock = 32mhz                                     '--> 32MHz   'configure the priority Config Priority = Static , Vector = Application , Lo = Enabled , Med = Enabled Enable Interrupts   Config Com7 = 57600 , Mode = Asynchroneous , Parity = None , Stopbits = 1 , Databits = 8 Waitms 2 Open "COM7:" For Binary As #1 Print #1 , Print #1 , "------------SPI MASTER-Slave Test----------------"     'We use Port D for SPI Config Pind.7 = Output Config Pind.6 = Input Config Pind.5 = Output Config Pind.4 = Output 'Bit7 = SCK = Output  ------> USCK (ATTINY85)   (PinB.2) 'Bit6 = MISO = Input  ------> DO   (ATTINY85)   (PinB.1) 'Bit5 = MOSI = Output ------> DI   (ATTINY85)   (PinB.0) 'Bit4 = SS = Output   ------> SS   (ATTINY85)   (PinB.4) Slave_select Alias Portd.4 Set Slave_select   Portd_pin4ctrl = Bits(3 , 4)                               ' Enalbe Pullup     Dim Bspivar As Byte Dim Spi_send_byte As Byte Dim Spi_receive_byte As Byte Dim Spi_master_want_send As Byte     'SPI, Master|Slave , MODE, clock division Config Spid = Hard , Master = Yes , Mode = 0 , Clockdiv = Clk128 , Data_order = Msb , Ss = Auto 'SS = Auto set the Slave Select (SS) automatically before a print #X or input #X command  (including initialization of the pin) 'Master SPI clock = 32MHz/Clk128 = 250KHz Open "SPID" For Binary As #12   Main:   Do   Wait 3                                                   'Every 3 seconds     Incr Spi_send_byte   Print #1 , "Spi_send_byte = " ; Spi_send_byte   'SEND TO SLAVE   Print #12 , Spi_send_byte                               'SEND one BYTE TO SLAVE     Waitms 10     Input #12 , Spi_receive_byte   Print #1 , Spi_receive_byte Loop       End                                                         'end program   'there is NO CLOSE for SPI       {{Languages}}

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Using USI (Universal Serial Interface)/de - Revision history

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Admin at 16:47, 13 February 2013