【正文】 dividebytwo flipflop, but minimum and maximum voltage high and low time specifications must be observed. Figure 1. Oscillator Connections Figure 2. External Clock Drive Configuration Idle Mode In idle mode, the CPU puts itself to sleep while all the onchip peripherals remain active. The mode is invoked by software. The content of the onchip RAM and all the special functions registers remain unchanged during this mode. The idle mode can be terminated by any enabled interrupt or by a hardware should be noted that when idle is terminated by a hard ware reset, the device normally resumes program execution,from where it left off, up to two machine cycles before the internal reset algorithm takes control. Onchip hardware inhibits access to internal RAM in this event, but access to the port pins is not inhibited. To eliminate the possibility of an unexpected write to a port pin when Idle is terminated by reset, the instruction following the one that invokes Idle should not be one that writes to a port pin or to external memory. Powerdown Mode 16 In the powerdown mode, the oscillator is stopped, and the instruction that invokes powerdown is the last instruction executed. The onchip RAM and Special Function Registers retain their values until the powerdown mode is terminated. The only exit from powerdown is a hardware reset. Reset redefines the SFRs but does not change the onchip RAM. The reset should not be activated before VCC is restored to its normal operating level and must be held active long enough to allow the oscillator to restart and stabilize. Program Memory Lock Bits On the chip are three lock bits which can be left unprogrammed (U) or can be programmed (P) to obtain the additional features listed in the table below. When lock bit 1 is programmed, the logic level at the EA pin is sampled and latched during reset. If the device is powered up without a reset, the latch initializes to a random value, and holds that value until reset is activated. It is necessary that the latched value of EA be in agreement with the current logic level at that pin in order for the device to function properly. Introduction Stepper motors are electromagic incrementalmotion devices which convert digital pulse inputs to analog angle outputs. Their inherent stepping ability allows for accurate position control without feedback. That is, they can track any step position in openloop mode, consequently no feedback is needed to implement position control. Stepper motors deliver higher peak 17 torque per unit weight than DC motors。 c frame to the q。 c reference, only two variables are independent (ia C ib C ic D 0)。 is its phase angle defined by φ = arctan(ω 1L1/R) . (16) Equations (12) and (13) indicate that multiple equilibria exist, which means that these equilibria can never be globally stable. One can see that there are two groups of equilibria as shown in Equations (12) and (13). The first group represented by Equation (12) corresponds to the real 24 operatingconditions of the motor. The second group represented by Equation (13) is always unstable and does not relate to the real operating conditions. In the following, we will concentrate on the equilibria represented by Equation (12). 25 開始 初始化 紅燈，等待 掃描鍵盤 是否有按鍵被按下 參數(shù)按鍵 轉(zhuǎn)向 開始鍵 是 數(shù)據(jù)鍵 轉(zhuǎn)向 處理 啟動 步進(jìn)電機(jī) 輸入下一組數(shù)據(jù) 確認(rèn)？ 改變速度？ 處理速度 步進(jìn)電機(jī)工作 一步結(jié)束 顯示 否 否 是 否 是 。 d frame can be obtained as vq = Riq + L1*diq/dt + NL1idω + Nλ 1ω , vd=Rid + L1*did/dt ? NL1iqω , (5) Figure 2. a, b, c and d, q reference frame. where L1 D L CM, and ! is the speed of the can be shown that the motor’s torque has the following form [2] T = 3/2Nλ 1iq The equation of motion of the rotor is written as J*dω /dt = 3/2*Nλ 1iq ? Bfω – Tl , where Bf is the coefficient of viscous friction, and Tl represents load torque, which is assumed to be a constant in this paper. In order to constitute the plete state equation of the motor, we need another state variable that represents the position of the rotor. For this purpose the so called load angle _ [8] is usually used, which satisfies the following equation Dδ /dt = ω ?ω 0 , where !0 is steadystate speed of the motor. Equations (5), (7), and (8) constitute the statespace model of the motor, for which the input variables are the voltages vq and vd. As mentioned before, stepper motors are fed by an inverter, whose output voltages are not sinusoidal but instead are square 22 waves. However, because the nonsinusoidal voltages do not change the oscillation feature and instability very much if pared to the sinusoidal case (as will be shown in Section 3, the oscillation is due to the nonlinearity of the motor), for the purposes of this paper we can assume the supply voltages are sinusoidal. Under this assumption, we can get vq and vd as follows vq = Vmcos(Nδ ) , vd = Vmsin(Nδ ) , where Vm is the maximum of the sine wave. With the above equation, we have changed the input voltages from a function of time to a function of state, and in this way we can represent the dynamics of the motor by a autonomous system, as shown below. This will simplify the mathematical analysis. From Equations (5), (7), and (8), the statespace model of the motor can be