Using ASEK Programmers with Long Harnesses and Capacitive Loads
Using ASEK Programmers with Long Harnesses and Capacitive Loads
韦德公共汽车，
Allegro MicroSystems, LLC
Introduction
Allegro的ASek编程套件允许用户轻松接口，程序和评估Allegro Sensor IC，以满足许多应用程序的需求。雷竞技最新网址Allegro的程序员旨在与特定于设备的子板一起工作。但是，它们通常用于与测试台和自定义模块接口。Allegro程序员和这些模块之间的链接可以是由长测试引线和外部元件组成的非理想设置，可以影响传输信号的质量。这些降级的信号可能阻碍程序员可靠地与Allegro传感器IC通信的能力。Allegro’s A1341 high-precision linear sensor ICwas used as the test IC for this report, but the concepts and techniques apply to a number of Allegro sensor IC families that follow a similar communication protocol.
测试设置
For the purpose of these tests, long leads (3 feet long), an interface box, and a custom device fixture (with 2 feet of wiring) were used to create a potentially non-ideal test setup. These conditions are similar to those that might be found in a laboratory environment. The block diagram in Figure 1 shows the connections used to interface the Allegro sensor IC with the ASEK Programmer.
An ASEK-05 was used for this evaluation; however, these same debugging techniques apply to Allegro’s ASEK-20 Programmer (a newer generation programmer).
图1: Test Schematic
除了长的引线和固定装置之外，还可以存在影响传输信号的传感器外部的许多组件。例如，A1341需要对PWM和发送操作的输出上的上拉电阻（由ASEK程序员提供）。对于下面记录的测试，在A1341的VCC和GND引脚之间连接10或100 NF旁路电容。
软件和ASEK程序员
Allegro开发了特定于设备的软件，与ASEK程序员合作。该软件可以在Allegro Microsystems软件门户上找到（雷竞技竞猜下载https://registration.allegromicro.com）。
对于这些测试，A1341样本程序员用于控制ASEK-05程序员。与A1341样本程序员和ASEK-05一起使用的设置如下图2所示。
图2.: Settings for 100 kbps with ASEK-05
典型的电容载荷
Under small capacitive loads (1 to 10 nF), the ASEK-05 can communicate with devices via Manchester at up to 100 kbps, even over long harness lengths. The oscilloscope plot in Figure 3 below shows a successful Manchester message over the long wire harness.
请注意，串行高电平完全一致到8 V，串行脉冲从未倾向于5 V.这些是Allegro的A1341线性传感器IC的所需水平。串行高和串行低级规格可能因设备系列而异。引用每个特定设备的数据表。
图4.shows how, at 100 kbps, the Manchester message degrades over a long harness with the use of 100 nF bypass capacitor.
A message in this form can periodically be interpreted by the device, but it is unreliable. The ringing is not desired, and the serial-low level may dip enough to momentarily turn off the device.
图3.: 100 kpbs Manchester with ASEK-05 and 10 nF bypass capacitor
图4.: Degraded Manchester sequence over long harness and 100 nF bypass capacitor at 100 kbps
ASEK Settings
本节将总结A1341样本程序员中提供的一些设置。目标是调整曼彻斯特通信，使得Allegro设备可以正确地读取，即使在具有大电容的长线束上也可以读取。
One parameter that can be changed is the Manchester communication speed. For the long wire and 100 nF capacitor condition, the Manchester communication speed was slowed to 40 kbps.
图5中的示波器图显示了所得波形。串行脉冲在A1341的正确水平下定居，但一些峰值仍然存在。可以改变的另一个参数是ASEK-05的转换速率。
The slew rate was reduced from 4 V/μs to 0.8 V/μs, significantly reducing peaking, as shown in Figure 6.
图5.: Manchester from ASEK-05 at 40 kbps with 100 nF bypass capacitor and long harness
图6：从ASEK-05成功的曼彻斯特消息，以40 kbps为设备，减速了100 NF旁路电容的转换速率
Reading Responses from the Device
ASEK程序员发送的消息仅是编程方程的一侧。以下部分将概述改进Allegro传感器IC返回ASEK程序员返回的读取消息的步骤。
参考，来自A1341的成功曼彻斯特响应如图7所示。
图7：A1341通过曼彻斯特回复阅读请求
The scope plot in Figure 8 shows how adding a load capacitor affects the response returned by the device. The light pink channel shows A1341 sensor IC’s response with a 1 nF load capacitor, while the dark red channel shows the response with a 10 nF load capacitor. These stacked plots clearly illustrate how the load capacitor impacts the device’s response.
图8：A1341通过曼彻斯特回复阅读请求
The device’s response with a 1 nF load was not ideal, but was read correctly by the ASEK programmer.
To improve the waveform under the 10 nF load condition, the communication speed was slowed down to 15 kbps under the Communications setup panel. This allowed the loaded output to return to an appropriate level. Still, the waveform was not ideal, but this can be correctly interpreted by the ASEK Programmer.
The threshold at which the ASEK compares the Manchester message was then lowered. “Threshold” was changed from 3 V to 2 V. The ASEK settings and resulting waveforms can be seen in Figure 9 and Figure 10.
图9.: ASEK settings used for A1341 with a 10 nF load capacitor
图10：A1341设备对具有10个NF负载电容的读取请求的响应
ASEK-20
一些设备系列都支持ASEK-05andASEK-20 programmers. The ASEK-20 was designed to be a flexible programming system to support multiple device families and protocols including I2C, SPI, and Manchester. Many of the settings are identical between ASEK-05 and ASEK-20, but the ASEK-20 Manchester speed is capped at a lower rate.
Conclusion
Allegro的ASek程序员旨在支持多个设备系列和数字通信协议;但是，外部连接和设备负载可能会影响成功编程的概率。ASEK程序员的默认设置并不总是有效地与设备通信。通信速度，转换速率和脉冲水平的正确组合可以在不同的条件下变化。
某些选项可能特定于特定设备，并且为一个家庭工作的设置可能无法与另一个家庭合作。
本文档中概述的技术是在非理想条件下增加Allegro的传感器IC和ASEK程序员之间通信可靠性的一般实践。
所有测试都是使用Allegro样本程序员进行A1341高精度线性霍尔效应传感器IC进行的。访问Allegro MicroSystem的软件门户（https://registration.allegromicro.com) to download the correct programming software for your Allegro sensor IC.