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ATMEGA8-16AI 参数 Datasheet PDF下载

ATMEGA8-16AI图片预览
型号: ATMEGA8-16AI
PDF下载: 下载PDF文件 查看货源
内容描述: 位的AVR微控制器8K字节在 - 系统内可编程Flash [-bit AVR Microcontroller with 8K Bytes In- System Programmable Flash]
分类和应用: 微控制器
文件页数/大小: 303 页 / 5122 K
品牌: ATMEL [ ATMEL ]
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Master Transmitter Mode  
In the Master Transmitter mode, a number of data bytes are transmitted to a Slave  
Receiver (see Figure 78). In order to enter a Master mode, a START condition must be  
transmitted. The format of the following address packet determines whether Master  
Transmitter or Master Receiver mode is to be entered. If SLA+W is transmitted, MT  
mode is entered, if SLA+R is transmitted, MR mode is entered. All the status codes  
mentioned in this section assume that the prescaler bits are zero or are masked to zero.  
Figure 78. Data Transfer in Master Transmitter Mode  
VCC  
Device 1  
MASTER  
TRANSMITTER  
Device 2  
SLAVE  
RECEIVER  
Device 3  
Device n  
R1  
R2  
........  
SDA  
SCL  
A START condition is sent by writing the following value to TWCR:  
TWCR  
TWINT  
TWEA  
TWSTA  
TWSTO  
TWWC  
TWEN  
TWIE  
value  
1
X
1
0
X
1
0
X
TWEN must be set to enable the Two-wire Serial Interface, TWSTA must be written to  
one to transmit a START condition and TWINT must be written to one to clear the  
TWINT Flag. The TWI will then test the Two-wire Serial Bus and generate a START  
condition as soon as the bus becomes free. After a START condition has been transmit-  
ted, the TWINT Flag is set by hardware, and the status code in TWSR will be 0x08 (see  
Table 66). In order to enter MT mode, SLA+W must be transmitted. This is done by writ-  
ing SLA+W to TWDR. Thereafter the TWINT bit should be cleared (by writing it to one)  
to continue the transfer. This is accomplished by writing the following value to TWCR:  
TWCR  
TWINT  
TWEA  
TWSTA  
TWSTO  
TWWC  
TWEN  
TWIE  
value  
1
X
0
0
X
1
0
X
When SLA+W have been transmitted and an acknowledgement bit has been received,  
TWINT is set again and a number of status codes in TWSR are possible. Possible sta-  
tus codes in Master mode are 0x18, 0x20, or 0x38. The appropriate action to be taken  
for each of these status codes is detailed in Table 66.  
When SLA+W has been successfully transmitted, a data packet should be transmitted.  
This is done by writing the data byte to TWDR. TWDR must only be written when  
TWINT is high. If not, the access will be discarded, and the Write Collision bit (TWWC)  
will be set in the TWCR Register. After updating TWDR, the TWINT bit should be  
cleared (by writing it to one) to continue the transfer. This is accomplished by writing the  
following value to TWCR:  
TWCR  
TWINT  
TWEA  
TWSTA  
TWSTO  
TWWC  
TWEN  
TWIE  
value  
1
X
0
0
X
1
0
X
176  
ATmega8(L)  
2486M–AVR–12/03  
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