User Manual

if i % 10 == 0 and i != 0:

print header,

if i % 5 == 0:

print " ",

s = "%02x" % ord(bytes[i])

if s == "00":

s = chr(250)*2

print s,

def CalculateChecksum(cmd):

assert((len(cmd) == length_packet - 1) or (len(cmd) ==

length_packet))

checksum = 0

for i in xrange(length_packet - 1):

checksum += ord(cmd[i])

checksum %= 256

return checksum

def main():

port = 3 # COM4 for my computer

baudrate = 38400

sp = serial.Serial(port, baudrate) # Open a serial connection

# Construct a set to remote command

cmd = chr(0xaa) + chr(0x00) + chr(0x20) # First three bytes

cmd += chr(0x01) + chr(0x00)*(length_packet - 1 - 4)

cmd += chr(CalculateChecksum(cmd))

assert(len(cmd) == length_packet)

# Send command to DC load

sp.write(cmd)

print "Set to remote command:"

DumpCommand(cmd)

# Get response from DC load

response = sp.read(length_packet)

assert(len(response) == length_packet)

print "Response:"

DumpCommand(response)

main()

The first three lines of the main() function set up a serial port to talk to. The next five lines construct

the string that we will send to the DC load. The chr() function creates a single character that has

the ASCII value of the argument. The + symbols allow strings to be concatenated. The expression

chr(0)*a_number creates a string of ASCII 0x00 characters whose length is a_number. . The last

character is the checksum of the previous 25 characters, calculated for us by the

CalculateChecksum() function.

When a command is sent to the instrument, you must always request for return data, which will

always be another 26 bytes. This is also dumped to the screen.

8500 DC Load Series Version: 030614 Page 49 of 77