Pololu Jrk USB - Manual (Page 32)

This command will turn the motor off by setting the Awaiting Command error bit. The jrk will not restart the motor
until it receives a Set Target command. The jrk can be configured to either brake or coast while the motor is off
(
Section 3.e ).
Set Target High Resolution
Compact protocol, binary: 110LLLLL, 0HHHHHHH
Compact protocol, hex: 0xC0 + target low 5 bits, target high 7 bits
Pololu protocol, binary: 10101010, device number, 010LLLLL, 0HHHHHHH
Pololu protocol, hex: 0xAA, device number, 0x40 + target low 5 bits, target high 7 bits
(where target is the 12-bit number HHHHHHHLLLLL)
This command clears the Awaiting Command error bit and (if Input Mode is Serial) lets you set the 12-bit target to
any of its allowed values (0–4095). The meaning of the target depends on what Feedback Mode the jrk is in (
Section
3.c ). The lower 5 bits of the command byte represent the lower 5 bits of the target, while the lower 7 bits of the data
byte represent the upper 7 bits of the target.
For example, if you want to set the target to 3229 ( 1100100 11101 in binary), you could send the following byte
sequence:
in binary: 110 11101 , 0 1100100
in hex: 0xDD, 0x64
in decimal: 221, 100
Here is some example C code that will generate the correct serial bytes, given an integer “target” that holds the desired
target (0–4095) and an array called serialBytes:
serialBytes[0] = 0xC0 + (target & 0x1F); // Command byte holds the lower 5 bits of target.
serialBytes[1] = (target >> 5) & 0x7F; // Data byte holds the upper 7 bits of target.
Many motor control applications do not need 12 bits of target resolution. If you want a simpler and lower-resolution
set of commands for setting the target, you can use the Set Target Low Resolution commands. Alternatively, you
could use the Set Target High Resolution command with the lower 5 bits of the target always zero: sending a 0xC0
byte followed by a data byte (0–127) will result in setting the target to a value of 32 multiplied by the data byte.
Set Target Low Resolution Forward
Compact protocol: 0xE1, magnitude
Pololu protocol: 0xAA, device number, 0x61, magnitude
This command clears the Awaiting Command error bit and (if Input Mode is Serial) sets the target to a value of 2048
or greater which is determined by the magnitude (0–127).
If the Feedback Mode is Analog or Tachometer, then the formula is
Target = 2048 + 16×magnitude.
If the Feedback Mode is None (speed control mode), then the formula is
Target = 2048 + (600/127)×magnitude.
This means that a magnitude of 127 will set the duty cycle target to full-speed forward (+600), while a magnitude of
zero will make the motor stop.
Pololu Jrk USB Motor Controller User's Guide © 2001–2014 Pololu Corporation
4. Using the Serial Interface Page 32 of 45