Pololu Simple Instrukcja Użytkownika Strona 85
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Oceniono. / 5. Na podstawie oceny klientów
basically a carryless long division of a CRC “polynomial”, 0x91, into your message (expressed as a continuous stream
of bits), where all you care about is the remainder. The Simple Motor Controller uses CRC-7, which means it uses an
8-bit polynomial and, as a result, produces a 7-bit remainder. This remainder is the lower 7 bits of the CRC byte you
tack onto the end of your command packets.
For sample C code that computes the CRC byte of a command packet, see Section 6.7.6.
The CRC implemented on the Simple Motor Controller is the same as the one on the Maestro
[http://www.pololu.com/product/1352] servo controller and jrk [http://www.pololu.com/product/1392] and qik
[http://www.pololu.com/product/1110] motor controllers, but it differs from that on the TReX
[http://www.pololu.com/product/777] motor controller. Instead of being done MSB first, the computation is
performed LSB first to match the order in which the bits are transmitted over the serial line. In standard
binary notation, the number 0x91 is written as 10010001. However, the bits are transmitted in this
order: 1, 0, 0, 0, 1, 0, 0, 1, so we will write it as 10001001 to carry out the computation below.
The CRC-7 algorithm is as follows:
1. Express your 8-bit CRC-7 polynomial and message in binary, LSB first. The polynomial 0x91 is written as
10001001.
2. Add 7 zeros to the end of your message.
3. Write your CRC-7 polynomial underneath the message so that the LSB of your polynomial is directly below
the LSB of your message.
4. If the LSB of your CRC-7 is aligned under a 1, XOR the CRC-7 with the message to get a new message; if
the LSB of your CRC-7 is aligned under a 0, do nothing.
5. Shift your CRC-7 right one bit. If all 8 bits of your CRC-7 polynomial still line up underneath message bits,
go back to step 4.
6. What’s left of your message is now your CRC-7 result (transmit these seven bits as your CRC byte when
talking to the Simple Motor Controller with CRC enabled).
If you have never encountered CRCs before, this probably sounds a lot more complicated than it really is. The
following example shows that the CRC-7 calculation is not that difficult. For the example, we will use a two-byte
sequence: 0x83, 0x01.
Steps 1 & 2 (write as binary, least significant bit first, add 7 zeros to the end of the message):
CRC-7 Polynomial = [1 0 0 0 1 0 0 1]
message = [1 1 0 0 0 0 0 1] [1 0 0 0 0 0 0 0] 0 0 0 0 0 0 0
Steps 3, 4, & 5:
_______________________________________________
1 0 0 0 1 0 0 1 ) 1 1 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0
XOR 1 0 0 0 1 0 0 1 | | | | | | | | | | | | | | |
_______________ | | | | | | | | | | | | | | |
1 0 0 1 0 0 0 1 | | | | | | | | | | | | | |
shift ----> 1 0 0 0 1 0 0 1 | | | | | | | | | | | | | |
_______________ | | | | | | | | | | | | | |
1 1 0 0 0 0 0 0 | | | | | | | | | | |
1 0 0 0 1 0 0 1 | | | | | | | | | | |
_______________ | | | | | | | | | | |
1 0 0 1 0 0 1 0 | | | | | | | | | |
1 0 0 0 1 0 0 1 | | | | | | | | | |
Pololu Simple Motor Controller User's Guide © 2001–2014 Pololu Corporation
6. Using the Serial Interface Page 85 of 101
- User's Guide 1
- 1. Overview 3
- Additional Features 4
- 1.1. 18v7 Included Hardware 6
- 1. Overview Page 9 of 101 9
- 2. Contacting Pololu 10
- 3. Getting Started 11
- Motor Limits 18
- Input Channels 18
- Conditions 18
- 3.4. Errors 20
- 3.5. LED Feedback 22
- Green USB LED 23
- Red Error LED 23
- Yellow Status LED 23
- Power Considerations 28
- Motor Considerations 29
- Power and Motor Connectors 30
- Logic Power 31
- Serial Connections Overview 33
- The ERR Pin in Detail 35
- The TXIN Pin in Detail 36
- RC Connections Overview 38
- Using the RC Channels 38
- Analog Connections Overview 41
- Using the Analog Channels 42
- 5.1. Input Settings 44
- Input Mode 45
- Mixing Mode 45
- Alternate Use 46
- Learn button 47
- Scaling Parameters 47
- 5.2. Motor Settings 49
- Hard Limits 49
- 5.3. Advanced Settings 51
- VIN Detection 52
- Over-temperature Response 53
- RC Pulse Detection 53
- Miscellaneous 53
- 5.4. Upgrading Firmware 54
- Firmware Versions 54
- Upgrade Instructions 54
- 6. Using the Serial Interface 56
- 6.1. Serial Settings 58
- 6.2. Binary Commands 59
- Compact Protocol 60
- Pololu Protocol 60
- Mini SSC Protocol 61
- Get Variable (any input mode) 66
- 30 + 256 * 1 = 286 67
- Stop Motor (any input mode) 70
- 6.3. ASCII Commands 71
- Command Format 71
- Command Strings 71
- Argument Strings 72
- Termination Characters 72
- Responses 72
- Using a Terminal Program 73
- 6.4. Controller Variables 78
- Status Flag Registers 78
- RC Channel Inputs 80
- Analog Channel Inputs 81
- Diagnostic Variables 82
- Temporary Motor Limits 83
- 6.6. Daisy Chaining 86
- Connections 87
- Sending commands 87
- 6.7. Sample Code 87
- 6.7.1. Arduino Examples 88
- Advanced Example 89
- 6.7.2. Orangutan Examples 91
- 6.7.4. Windows C Example 98
- 6.7.5. Bash Script Example 98
- 6.7.6. CRC Computation in C 99
- Native USB Interface 101
- Virtual Serial Port 101
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