* : Products list (parametric search)
* : Products list (parametric search)
* : Products list (parametric search)
* : Products list (parametric search)
* : Products list (parametric search)
* : Products list (parametric search)
* : Products list (parametric search)
* : Products list (parametric search)
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The information presented in this cross reference is based on TOSHIBA's selection criteria and should be treated as a suggestion only. Please carefully review the latest versions of all relevant information on the TOSHIBA products, including without limitation data sheets and validate all operating parameters of the TOSHIBA products to ensure that the suggested TOSHIBA products are truly compatible with your design and application.Please note that this cross reference is based on TOSHIBA's estimate of compatibility with other manufacturers' products, based on other manufacturers' published data, at the time the data was collected.TOSHIBA is not responsible for any incorrect or incomplete information. Information is subject to change at any time without notice.
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该器件可以轻松实现双向切换,但必须注意总线缓冲器输出冲突和输入悬空。
尽管该总线缓冲器允许轻松实现信号方向的切换,但仍需考虑以下几点:
图1所示为双向总线缓冲器的等效电路(74VHC245),表1所示为真值表。.
当/G为“H”电平时,所有输入/输出端子均悬空,因此需要上拉至电源或下拉至GND。
表1:双向总线缓冲器真值表(74VHC245)
下面用图2所示的电路和时序图说明了时序要求。
A总线和B总线之间连接了一个双向总线缓冲器。在初始状态下,A引脚为输入端,B引脚为输出端。因此,信号从A总线传输至B总线。此时,缓冲器Y为禁用状态(即不提供输出)。
1.将/G引脚设为高电平,以禁用双向总线缓冲器。禁用总线缓冲区需经过一段时间tpLZ。随后,A引脚和B引脚均呈现高阻态。因此,有必要将上拉电阻(Rpullup1和Rpullup2)连接至这些引脚,以稳定其电位。具有总线保持功能的总线缓冲器无需任何上拉电阻器。
2.信号方向改变后输出发生冲突。因此,在禁用总线缓冲器的同时,禁用缓冲器X的输出并启用缓冲器Y的输出。此外,在此期间将方向引脚(DIR)从低电平设为高电平。
3.将/G引脚设为低电平,以启用总线缓冲器。
当DIR引脚改变状态(从低电平变为高电平,或从高电平变为低电平)并且使能引脚(/G或/OE)改变状态时,内部电路会改变其模式。在此期间,输出值不确定,即无法确定输出为高电平、低电平还是介于高电平与低电平之间。请在设计时考虑到这一点,因为这些时间段内的输出值无法得到保证。
以下文档也包含相关信息。