参数资料
| 型号： | ATMEGA645-16AI |
| 厂商： | Atmel |
| 文件页数： | 33/85页 |
| 文件大小： | 0K |
| 描述： | IC AVR MCU FLASH 64K 5V 64TQFP |
| 产品培训模块： | megaAVR Introduction |
| 标准包装： | 90 |
| 系列： | AVR® ATmega |
| 核心处理器： | AVR |
| 芯体尺寸： | 8-位 |
| 速度： | 16MHz |
| 连通性： | SPI，UART/USART，USI |
| 外围设备： | 欠压检测/复位，POR，PWM，WDT |
| 输入/输出数： | 53 |
| 程序存储器容量： | 64KB（32K x 16） |
| 程序存储器类型： | 闪存 |
| EEPROM 大小： | 2K x 8 |
| RAM 容量： | 4K x 8 |
| 电压 - 电源 (Vcc/Vdd)： | 2.7 V ~ 5.5 V |
| 数据转换器： | A/D 8x10b |
| 振荡器型： | 内部 |
| 工作温度： | -40°C ~ 85°C |
| 封装/外壳： | 64-TQFP |
| 包装： | 托盘 |
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PIC16(L)F1824/1828
DS41419C-page 256
Preliminary
2010-2011 Microchip Technology Inc.
When one device is transmitting a logical one, or letting
the line float, and a second device is transmitting a log-
ical zero, or holding the line low, the first device can
detect that the line is not a logical one. This detection,
when used on the SCL line, is called clock stretching.
Clock stretching gives slave devices a mechanism to
control the flow of data. When this detection is used on
the SDA line, it is called arbitration. Arbitration ensures
that there is only one master device communicating at
any single time.
25.3.1
CLOCK STRETCHING
When a slave device has not completed processing
data, it can delay the transfer of more data through the
process of Clock Stretching. An addressed slave
device may hold the SCL clock line low after receiving
or sending a bit, indicating that it is not yet ready to con-
tinue. The master that is communicating with the slave
will attempt to raise the SCL line in order to transfer the
next bit, but will detect that the clock line has not yet
been released. Because the SCL connection is
open-drain, the slave has the ability to hold that line low
until it is ready to continue communicating.
Clock stretching allows receivers that cannot keep up
with a transmitter to control the flow of incoming data.
25.3.2
ARBITRATION
Each master device must monitor the bus for Start and
Stop bits. If the device detects that the bus is busy, it
cannot begin a new message until the bus returns to an
Idle state.
However, two master devices may try to initiate a trans-
mission on or about the same time. When this occurs,
the process of arbitration begins. Each transmitter
checks the level of the SDA data line and compares it
to the level that it expects to find. The first transmitter to
observe that the two levels don’t match, loses arbitra-
tion, and must stop transmitting on the SDA line.
For example, if one transmitter holds the SDA line to a
logical one (lets it float) and a second transmitter holds
it to a logical zero (pulls it low), the result is that the
SDA line will be low. The first transmitter then observes
that the level of the line is different than expected and
concludes that another transmitter is communicating.
The first transmitter to notice this difference is the one
that loses arbitration and must stop driving the SDA
line. If this transmitter is also a master device, it also
must stop driving the SCL line. It then can monitor the
lines for a Stop condition before trying to reissue its
transmission. In the meantime, the other device that
has not noticed any difference between the expected
and actual levels on the SDA line continues with its
original transmission. It can do so without any compli-
cations, because so far, the transmission appears
exactly as expected with no other transmitter disturbing
the message.
Slave Transmit mode can also be arbitrated, when a
master addresses multiple slaves, but this is less com-
mon.
If two master devices are sending a message to two dif-
ferent slave devices at the address stage, the master
sending the lower slave address always wins arbitra-
tion. When two master devices send messages to the
same slave address, and addresses can sometimes
refer to multiple slaves, the arbitration process must
continue into the data stage.
Arbitration usually occurs very rarely, but it is a neces-
sary process for proper multi-master support.
25.4
I2C
Mode Operation
All MSSP1 I2C communication is byte oriented and
shifted out MSb first. Six SFR registers and 2 interrupt
flags interface the module with the PIC microcon-
troller and user software. Two pins, SDA and SCL, are
exercised by the module to communicate with other
external I2C devices.
25.4.1 BYTE FORMAT
All communication in I2C is done in 9-bit segments. A
byte is sent from a Master to a Slave or vice-versa, fol-
lowed by an Acknowledge bit sent back. After the 8th
falling edge of the SCL line, the device outputting data
on the SDA changes that pin to an input and reads in
an acknowledge value on the next clock pulse.
The clock signal, SCL, is provided by the master. Data
is valid to change while the SCL signal is low, and
sampled on the rising edge of the clock. Changes on
the SDA line while the SCL line is high define special
conditions on the bus, explained below.
25.4.2 DEFINITION OF I2C TERMINOLOGY
There is language and terminology in the description
of I2C communication that have definitions specific to
I2C. That word usage is defined below and may be
used in the rest of this document without explana-
tion.
This table was adapted from the Phillips I2C
specification.
25.4.3 SDA AND SCL PINS
Selection of any I2C mode with the SSP1EN bit set,
forces the SCL and SDA pins to be open-drain. These
pins should be set by the user to inputs by setting the
appropriate TRIS bits.
Note: Data is tied to output zero when an I2C
mode is enabled.
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相关代理商/技术参数 |
参数描述 |
|---|---|
| ATmega645-16AU | 功能描述:8位微控制器 -MCU 64kB Flash 2kB EEPROM 54 I/O Pins RoHS:否 制造商:Silicon Labs 核心:8051 处理器系列:C8051F39x 数据总线宽度:8 bit 最大时钟频率:50 MHz 程序存储器大小:16 KB 数据 RAM 大小:1 KB 片上 ADC:Yes 工作电源电压:1.8 V to 3.6 V 工作温度范围:- 40 C to + 105 C 封装 / 箱体:QFN-20 安装风格:SMD/SMT |
| ATMEGA645-16AUR | 功能描述:8位微控制器 -MCU AVR 64KB FLSH 2KB EE 4KB SRAM-16MHz, 5V RoHS:否 制造商:Silicon Labs 核心:8051 处理器系列:C8051F39x 数据总线宽度:8 bit 最大时钟频率:50 MHz 程序存储器大小:16 KB 数据 RAM 大小:1 KB 片上 ADC:Yes 工作电源电压:1.8 V to 3.6 V 工作温度范围:- 40 C to + 105 C 封装 / 箱体:QFN-20 安装风格:SMD/SMT |
| ATmega645-16MI | 功能描述:8位微控制器 -MCU AVR 64K FLASH 2K EE 4K SRAM ADC RoHS:否 制造商:Silicon Labs 核心:8051 处理器系列:C8051F39x 数据总线宽度:8 bit 最大时钟频率:50 MHz 程序存储器大小:16 KB 数据 RAM 大小:1 KB 片上 ADC:Yes 工作电源电压:1.8 V to 3.6 V 工作温度范围:- 40 C to + 105 C 封装 / 箱体:QFN-20 安装风格:SMD/SMT |
| ATmega645-16MU | 功能描述:8位微控制器 -MCU AVR 64K FLASH 2K EE 4K SRAM ADC RoHS:否 制造商:Silicon Labs 核心:8051 处理器系列:C8051F39x 数据总线宽度:8 bit 最大时钟频率:50 MHz 程序存储器大小:16 KB 数据 RAM 大小:1 KB 片上 ADC:Yes 工作电源电压:1.8 V to 3.6 V 工作温度范围:- 40 C to + 105 C 封装 / 箱体:QFN-20 安装风格:SMD/SMT |
| ATMEGA645-16MUR | 功能描述:8位微控制器 -MCU AVR 64KB FLSH 2KB EE 4KB SRAM-16MHz, 5V RoHS:否 制造商:Silicon Labs 核心:8051 处理器系列:C8051F39x 数据总线宽度:8 bit 最大时钟频率:50 MHz 程序存储器大小:16 KB 数据 RAM 大小:1 KB 片上 ADC:Yes 工作电源电压:1.8 V to 3.6 V 工作温度范围:- 40 C to + 105 C 封装 / 箱体:QFN-20 安装风格:SMD/SMT |
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