ATmega16 datasheet(149/357 Pages) ATMEL

149 / 357 page

149

2466S–AVR–05/09

ATmega16(L)

IDLE

No transfers on the communication line (RxD or TxD). An IDLE line must be

high.

The frame format used by the USART is set by the UCSZ2:0, UPM1:0, and USBS bits in

UCSRB and UCSRC. The Receiver and Transmitter use the same setting. Note that changing

the setting of any of these bits will corrupt all ongoing communication for both the Receiver and

Transmitter.

The USART Character SiZe (UCSZ2:0) bits select the number of data bits in the frame. The

USART Parity mode (UPM1:0) bits enable and set the type of parity bit. The selection between

one or two stop bits is done by the USART Stop Bit Select (USBS) bit. The receiver ignores the

second stop bit. An FE (Frame Error) will therefore only be detected in the cases where the first

stop bit is zero.

Parity Bit Calculation

The parity bit is calculated by doing an exclusive-or of all the data bits. If odd parity is used, the

result of the exclusive or is inverted. The relation between the parity bit and data bits is as

follows::

even

Parity bit using even parity

odd

Parity bit using odd parity

Data bit n of the character

If used, the parity bit is located between the last data bit and first stop bit of a serial frame.

USART

Initialization

The USART has to be initialized before any communication can take place. The initialization pro-

cess normally consists of setting the baud rate, setting frame format and enabling the

Transmitter or the Receiver depending on the usage. For interrupt driven USART operation, the

Global Interrupt Flag should be cleared (and interrupts globally disabled) when doing the

initialization.

Before doing a re-initialization with changed baud rate or frame format, be sure that there are no

ongoing transmissions during the period the registers are changed. The TXC Flag can be used

to check that the Transmitter has completed all transfers, and the RXC Flag can be used to

check that there are no unread data in the receive buffer. Note that the TXC Flag must be

cleared before each transmission (before UDR is written) if it is used for this purpose.

The following simple USART initialization code examples show one assembly and one C func-

tion that are equal in functionality. The examples assume asynchronous operation using polling

(no interrupts enabled) and a fixed frame format. The baud rate is given as a function parameter.

For the assembly code, the baud rate parameter is assumed to be stored in the r17:r16 regis-

ters. When the function writes to the UCSRC Register, the URSEL bit (MSB) must be set due to

the sharing of I/O location by UBRRH and UCSRC.

Peven

dn 1

–

…

Podd

⊕

⊕⊕⊕⊕⊕

dn 1

–

…

⊕

⊕⊕⊕⊕⊕

ATmega16 датащи(PDF) 149 Page - ATMEL Corporation

ATmega16 датащи(HTML) 149 Page - ATMEL Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

датащи скачать

ссылки URL