HFAS11S伺服模块，TOSHIBA数据库
由于32位处理器的价格不断下降，用户已可以大量使用，而32位RISC处理器则更是受到青睐，并将在某些领域替代原来的8位单片机。其中，微处理器系列处于领先地位。笔者所介绍的数据采集系统中采用的是PHILIPS公司生产的以ARM7处理器作为内核的LPC2104单片机。 1 MAX194简介
HFAS11S伺服模块，TOSHIBA数据库 MAX194是MAXIM公司推出的一种逐次逼近型模数转换器(ADC)，具有高速、高精度、低功耗等特点。MAX194内部设有校准电路，用于保证全温度范围内的线性度，从而维持全量程内的高性能，且不需要外部的调整电路。分开的模拟和数字供电最大程度地减少了数字噪声耦合。在转换过程中，每转换完成一个，数据位就输出一位。此时，SCLK应该接地，CLK既作为ADC的转换时钟又作为串行接口的移位输出时钟。
◇ 异步模式：单片机只能在MAX194完成一次转换之后才能将转换结果读出，然后再启动下一次转换。这种模式降低了MAX194连续转换的速度。
1．3 硬件接口
串行接口标准与SPITM、QSPITM兼容。MAX194在进行A/D转换时需要由外部提供时钟信号。图2是MAX194与单片机采用异步模式的硬件连接图。该图中，MAX194进行A/D转换所需的时钟信号由外部晶振分频得到。使用者也可根据需要由单片机提供该时钟信号。时钟信号的最大频率是1.7 MHz，参考电压的范围是0～VDDA+0.3 V。为了防止从AIN端输入的信号损坏ADC，应在信号输入端加电压限幅电路以保护MAX194。图3是其时序图。P3.0产生的START信号与CLK信号相“或”后作为启动转换的CONV信号。CONV的下降沿可以启动转换，开始转换后监测EOC，当它由高电平变低时说明转换已经结束，适当延时后就可以从串口读出转换结果，读数据的最高速率是4.19 Mbps。其中后两项是测试全显电流和段电流的有效值。由于液晶屏的背电极和段电极之间是灌注了液晶材料的，因此在外加电压驱动下，可等效为一个电容性负载。所以，液晶屏的电流采样电路是一个典型的微分电路，其输出电压是一个窄脉冲序列，使用RMS/DC转换集成电路AD536A可以实时测试不同窄脉冲电压的有效值。
1 液晶屏测试仪的系统组成
debugging, PLC programming software should be used first. These programming software can monitor the state of each variable and program diagram, which is the basic function, otherwise it cannot be debugged. For most slow and simple logic, the basic function of programming software is enough to complete the debugging task. If the logic is complex, spans many pages, or the signal changes quickly, it is very difficult to observe the real-time state with the naked eye and think logically. Most of the programming software will provide variable monitoring tables, put in all the variables that need to be concerned, and click monitoring to refresh the status in real time, which can solve the problem of monitoring a large number of variables to a certain extent. However, for programs with complex logic or fast change speed, we need to use the tool of sequence diagram to record the change process and analyze it slowly afterwards.Also, for the simple example of pump control above, if there is a phenomenon that the pump will occasionally stop before reaching the low liquid level after starting, what is the reason? It may be the jitter of the low liquid level signal, or the loose wiring of the output, etc. at this time, it is easy to judge if you can get the time sequence diagram at that time. If the sequence diagram is shown in Figure 2, we can judge that it is caused by the unreliability of the low liquid level signal. Just check the wiring of the low liquid level signal or the float switch. If the sequence diagram is shown in Figure 3, it is necessary to check the output wiring of the control command and the main circuit of the motor.
