atmega32u4-16mu ATMEL Corporation, atmega32u4-16mu Datasheet - Page 234

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

20.3
20.4
234
SPI Data Modes and Timing
Frame Formats
ATmega32U4
Note:
There are four combinations of XCKn (SCK) phase and polarity with respect to serial data, which
are determined by control bits UCPHAn and UCPOLn. The data transfer timing diagrams are
shown in
signal, ensuring sufficient time for data signals to stabilize. The UCPOLn and UCPHAn function-
ality is summarized in
all ongoing communication for both the Receiver and Transmitter.
Table 20-2.
Figure 20-1. UCPHAn and UCPOLn data transfer timing diagrams.
A serial frame for the MSPIM is defined to be one character of 8 data bits. The USART in MSPIM
mode has two valid frame formats:
A frame starts with the least or most significant data bit. Then the next data bits, up to a total of
eight, are succeeding, ending with the most or least significant bit accordingly. When a complete
frame is transmitted, a new frame can directly follow it, or the communication line can be set to
an idle (high) state.
• 8-bit data with MSB first
• 8-bit data with LSB first
UCPOLn
BAUD
f
UBRRn
0
0
1
1
OSC
Data setup (TXD)
Data sample (RXD)
XCK
XCK
Data setup (TXD)
Data sample (RXD)
1. The baud rate is defined to be the transfer rate in bit per second (bps)
Figure
UCPOLn and UCPHAn Functionality-
20-1. Data bits are shifted out and latched in on opposite edges of the XCKn
UCPHAn
0
1
0
1
Table
Baud rate (in bits per second, bps)
System Oscillator clock frequency
Contents of the UBRRnH and UBRRnL Registers, (0-4095)
UCPOL=0
20-2. Note that changing the setting of any of these bits will corrupt
SPI Mode
0
1
2
3
Leading Edge
Sample (Rising)
Setup (Rising)
Sample (Falling)
Setup (Falling)
Data setup (TXD)
Data setup (TXD)
XCK
Data sample (RXD)
XCK
Data sample (RXD)
Trailing Edge
Setup (Falling)
Sample (Falling)
Setup (Rising)
Sample (Rising)
UCPOL=1
7766A–AVR–03/08