參數(shù)資料
型號(hào): ATMEGA649V-8AI
廠商: Atmel
文件頁數(shù): 35/146頁
文件大?。?/td> 0K
描述: IC AVR MCU FLASH 64K 1.8V 64TQFP
產(chǎn)品培訓(xùn)模塊: megaAVR Introduction
標(biāo)準(zhǔn)包裝: 90
系列: AVR® ATmega
核心處理器: AVR
芯體尺寸: 8-位
速度: 8MHz
連通性: SPI,UART/USART,USI
外圍設(shè)備: 欠壓檢測/復(fù)位,LCD,POR,PWM,WDT
輸入/輸出數(shù): 53
程序存儲(chǔ)器容量: 64KB(32K x 16)
程序存儲(chǔ)器類型: 閃存
EEPROM 大小: 2K x 8
RAM 容量: 4K x 8
電壓 - 電源 (Vcc/Vdd): 1.8 V ~ 5.5 V
數(shù)據(jù)轉(zhuǎn)換器: A/D 8x10b
振蕩器型: 內(nèi)部
工作溫度: -40°C ~ 85°C
封裝/外殼: 64-TQFP
包裝: 托盤
PIC16(L)F1825/1829
DS41440C-page 282
2010-2012 Microchip Technology Inc.
25.6.13.1
Bus Collision During a Start
Condition
During a Start condition, a bus collision occurs if:
a)
SDAx or SCLx are sampled low at the beginning
of the Start condition (Figure 25-33).
b)
SCLx is sampled low before SDAx is asserted
During a Start condition, both the SDAx and the SCLx
pins are monitored.
If the SDAx pin is already low, or the SCLx pin is
already low, then all of the following occur:
the Start condition is aborted,
the BCLxIF flag is set and
the MSSPx module is reset to its Idle state
The Start condition begins with the SDAx and SCLx
pins deasserted. When the SDAx pin is sampled high,
the Baud Rate Generator is loaded and counts down. If
the SCLx pin is sampled low while SDAx is high, a bus
collision occurs because it is assumed that another
master is attempting to drive a data ‘1’ during the Start
condition.
If the SDAx pin is sampled low during this count, the
BRG is reset and the SDAx line is asserted early
(Figure 25-35). If, however, a ‘1’ is sampled on the
SDAx pin, the SDAx pin is asserted low at the end of
the BRG count. The Baud Rate Generator is then
reloaded and counts down to zero; if the SCLx pin is
sampled as ‘0’ during this time, a bus collision does not
occur. At the end of the BRG count, the SCLx pin is
asserted low.
FIGURE 25-33:
BUS COLLISION DURING START CONDITION (SDAX ONLY)
Note:
The reason that bus collision is not a
factor during a Start condition is that no
two bus masters can assert a Start
condition at the exact same time.
Therefore, one master will always assert
SDAx before the other. This condition
does not cause a bus collision because
the two masters must be allowed to
arbitrate the first address following the
Start condition. If the address is the same,
arbitration must be allowed to continue
into the data portion, Repeated Start or
Stop conditions.
SDAx
SCLx
SEN
SDAx sampled low before
SDAx goes low before the SEN bit is set.
S bit and SSPxIF set because
SSPx module reset into Idle state.
SEN cleared automatically because of bus collision.
S bit and SSPxIF set because
Set SEN, enable Start
condition if SDAx = 1, SCLx = 1
SDAx = 0, SCLx = 1.
BCLxIF
S
SSPxIF
SDAx = 0, SCLx = 1.
SSPxIF and BCLxIF are
cleared by software
SSPxIF and BCLxIF are
cleared by software
Set BCLxIF,
Start condition. Set BCLxIF.
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