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EPM1270T100C 数据表(PDF) 39 Page - Altera Corporation |
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EPM1270T100C 数据表(HTML) 39 Page - Altera Corporation |
39 / 86 page Chapter 2: MAX II Architecture 2–31 I/O Structure © October 2008 Altera Corporation MAX II Device Handbook Bus Hold Each MAX II device I/O pin provides an optional bus-hold feature. The bus-hold circuitry can hold the signal on an I/O pin at its last-driven state. Since the bus-hold feature holds the last-driven state of the pin until the next input signal is present, an external pull-up or pull-down resistor is not necessary to hold a signal level when the bus is tri-stated. The bus-hold circuitry also pulls undriven pins away from the input threshold voltage where noise can cause unintended high-frequency switching. The designer can select this feature individually for each I/O pin. The bus-hold output will drive no higher than VCCIO to prevent overdriving signals. If the bus-hold feature is enabled, the device cannot use the programmable pull-up option. The bus-hold circuitry uses a resistor to pull the signal level to the last driven state. The DC and Switching Characteristics chapter in the MAX II Device Handbook gives the specific sustaining current for each VCCIO voltage level driven through this resistor and overdrive current used to identify the next-driven input level. The bus-hold circuitry is only active after the device has fully initialized. The bus-hold circuit captures the value on the pin present at the moment user mode is entered. Programmable Pull-Up Resistor Each MAX II device I/O pin provides an optional programmable pull-up resistor during user mode. If the designer enables this feature for an I/O pin, the pull-up resistor holds the output to the VCCIO level of the output pin’s bank. 1 The programmable pull-up resistor feature should not be used at the same time as the bus-hold feature on a given I/O pin. Programmable Input Delay The MAX II IOE includes a programmable input delay that is activated to ensure zero hold times. A path where a pin directly drives a register, with minimal routing between the two, may require the delay to ensure zero hold time. However, a path where a pin drives a register through long routing or through combinational logic may not require the delay to achieve a zero hold time. The Quartus II software uses this delay to ensure zero hold times when needed. MultiVolt I/O Interface The MAX II architecture supports the MultiVolt I/O interface feature, which allows MAX II devices in all packages to interface with systems of different supply voltages. The devices have one set of VCC pins for internal operation (VCCINT), and up to four sets for input buffers and I/O output driver buffers (VCCIO), depending on the number of I/O banks available in the devices where each set of VCC pins powers one I/O bank. The EPM240 and EPM570 devices have two I/O banks respectively while the EPM1270 and EPM2210 devices have four I/O banks respectively. |
类似零件编号 - EPM1270T100C |
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类似说明 - EPM1270T100C |
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