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I am having trouble figuring out how to send a negative number over C# UWP SerialDevice DataWriter object

I am using Windows 10 IOT Core with Raspberry PI 2 B. I am trying to control a Sabertooth 2x25 Motor Driver using packetized serial https://www.dimensionengineering.com/datasheets/Sabertooth2x25.pdf . The documentation describes the communication as: The packet format for the Sabertooth consists of an address byte, a command byte, a data byte and a seven bit checksum. Address bytes have value greater than 128, and all subsequent bytes have values 127 or lower. This allows multiple types of devices to share the same serial line. And an example:

Packet

Address: 130

Command : 0

Data: 64

Checksum: 66

The databyte can be -127 to 127. The description states that the Data byte is one byte but when I try to convert a negative number to a byte in C# I get an overflow exception because of the sign bit (I think).

Psuedo Code provided in manual

Void DriveForward(char address, char speed)
{
Putc(address);
Putc(0);
Putc(speed);
Putc((address + 0 + speed) & 0b01111111);
}

What would be the best method to write the Data to the DataWriter Object of SerialDevice taking into account negative numbers. I am also open to using a differnt method other than DataWriter to complete the task.

ProgrammingLlama
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pleslie
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  • I asked a stupid question. I got -127 to 127 based on some of the manufacturers sample code for use with their driver (which I can't use because it isnt UWP compatible). I just realized that what their driver is probably doing is if you call one of their driver functions Drive(address, speed) it uses the reverse command for negative numbers(removes the sign and goes in reverse at that speed) and forward command for positive numbers. – pleslie Aug 21 '19 at 01:09
  • So have you fixed the issue? If not please feel free let me know. – Michael Xu Aug 21 '19 at 02:40

1 Answers1

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I asked a stupid question. I got -127 to 127 based on some of the manufacturers sample code for use with their driver (which I can't use because it isnt UWP compatible). I just realized that what their driver is probably doing is if you call one of their driver functions Drive(address, speed) it uses the reverse command for negative numbers(removes the sign and goes in reverse at that speed) and forward command for positive numbers. –

pleslie
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