KVASER CANlib & Python第3部分：U100和Python

U100 LEDs

与以前的设备上拥有的三种颜色（黄色、红色和绿色）不同，U100具有五种颜色。这些颜色包括：黄色、绿色、红色、白色和蓝色。LED条具有两个状态区域，如图所示，每条指示灯有一个状态区域。

当首次连接U100时，两个LED条会先缓慢闪烁一次绿光，然后状态区域会亮起白光。当通道上线时，白色状态区域将变为绿色。当U100接收或发送报文时，其中一个状态区域将闪烁黄色。如果设备接收到报文，RX状态区域将闪烁黄色。如果设备发送报文，TX状态区域将闪烁黄色。如果在传输过程中出现错误，LED将在一定程度上显示我们接收到的错误类型。如果我们尝试在总线上没有其他通道的情况下使用U100发送报文时，通道将进入错误被动状态，两个状态区域都会闪烁红色。此外，由于通道正在传输错误帧，TX LED条将变为红色。如果我们尝试以不匹配的比特率读取报文，状态区域仍将闪烁红色。但是由于我们现在正在接收错误帧，RX LED条将变为红色，而不是TX灯条。

如果我们增加总线负载（增加发送的报文数量），LED指示灯也会随之亮起。根据总线负载的不同，从TX或RX LED的状态区域开始，更多的LED将亮起黄光，这取决于我们是在发送还是接收。要测试LED，我们可以编写以下脚本并将其命名为u100.py。

import time
from canlib import canlib, Frame

# First create two frames with different id:s.
frame_a = Frame(id_=1, data=[72, 69, 76, 76, 79, 33])
frame_b = Frame(id_=2, data=[72, 69, 76, 76, 79, 33])

# Second, open two channels, one for the U100 and one for another interface.
# In this example the U100 is connected to channel 3 and a USBcan is
# connected to channel 2. And set their bitrate.
ch_a = canlib.openChannel(channel=2, bitrate=canlib.Bitrate.BITRATE_100K)
ch_b = canlib.openChannel(channel=3, bitrate=canlib.Bitrate.BITRATE_100K)

#set both channels to normal and go on bus.
ch_a.setBusOutputControl(canlib.Driver.NORMAL)
ch_b.setBusOutputControl(canlib.Driver.NORMAL)
ch_a.busOn()
ch_b.busOn()

# To get a clearer sense of what happens, you will need to press enter between
# each test.
input("Press enter to continue")
# In the first example we will transmit messages with the U100. In the
# second example we will receive messages with the U100. And in the third
# and last example we will both send and receive messages with the U100.
# In all examples we will send 50 messages, you can test to increase this
# number to see its effect.
for i in range(50):
# We will make use of the try function during these tests. The program will
# try to execute the commands within the try-block (the indented region
# underneath). If the program encounters an CanGeneralError (indicated by
# the except command) the program will instead execute the commands within
# the except block. In this example the messages might be sent to quickly
# and result in a CanGeneralError which is why we will wait for 0.1 seconds
# with time.sleep if this happens.
    try:
        # This is the try-block.
        ch_b.write(frame_b)
        ch_a.read(1000)
    except canlib.exceptions.CanGeneralError:
        # This is the except block.
        time.sleep(0.1)

input("Press enter to continue")

for i in range(50):
    try:
        ch_a.write(frame_a)
        ch_b.read(1000)
    except canlib.exceptions.CanGeneralError:
        time.sleep(0.1)

input("Press enter to continue")

for i in range(50):
    try:
        ch_b.write(frame_b)
        ch_a.read(1000)
        ch_a.write(frame_a)
        ch_b.read(1000)
    except canlib.exceptions.CanGeneralError:
        time.sleep(0.1)

ch_a.close()
ch_b.close()