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EP1K50 数据表(PDF) 23 Page - Altera Corporation |
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EP1K50 数据表(HTML) 23 Page - Altera Corporation |
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23 / 86 page  Altera Corporation 23 ACEX 1K Programmable Logic Device Family Data Sheet 13 Clearable Counter Mode The clearable counter mode is similar to the up/down counter mode, but it supports a synchronous clear instead of the up/down control. The clear function is substituted for the cascade-in signal in the up/down counter mode. Two 3-input LUTs are used; one generates the counter data, and the other generates the fast carry bit. Synchronous loading is provided by a 2-to-1 multiplexer. The output of this multiplexer is AND ed with a synchronous clear signal. Internal Tri-State Emulation Internal tri-state emulation provides internal tri-states without the limitations of a physical tri-state bus. In a physical tri-state bus, the tri-state buffers’ output enable (OE) signals select which signal drives the bus. However, if multiple OE signals are active, contending signals can be driven onto the bus. Conversely, if no OE signals are active, the bus will float. Internal tri-state emulation resolves contending tri-state buffers to a low value and floating buses to a high value, thereby eliminating these problems. The Altera software automatically implements tri-state bus functionality with a multiplexer. Clear & Preset Logic Control Logic for the programmable register’s clear and preset functions is controlled by the DATA3, LABCTRL1, and LABCTRL2 inputs to the LE. The clear and preset control structure of the LE asynchronously loads signals into a register. Either LABCTRL1 or LABCTRL2 can control the asynchronous clear. Alternatively, the register can be set up so that LABCTRL1 implements an asynchronous load. The data to be loaded is driven to DATA3; when LABCTRL1 is asserted, DATA3 is loaded into the register. During compilation, the compiler automatically selects the best control signal implementation. Because the clear and preset functions are active- low, the Compiler automatically assigns a logic high to an unused clear or preset. The clear and preset logic is implemented in one of the following six modes chosen during design entry: ■ Asynchronous clear ■ Asynchronous preset ■ Asynchronous clear and preset ■ Asynchronous load with clear ■ Asynchronous load with preset ■ Asynchronous load without clear or preset |
类似零件编号 - EP1K50 |
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类似说明 - EP1K50 |
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