27961 Parallax Inc, 27961 Datasheet - Page 12

• Manufacturer Part Number: 27961
• Description: MODULE MOTOR MIND SIP
• Manufacturer: Parallax Inc

Specifications of 27961

• Product: Microcontroller Accessories
• Operating Supply Voltage: 6 to 36 V
• Board Size: 30.48 mm x 25.4 mm
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Motor Mind B enhanced
Data Sheet
4.5 REV Command
The REV command will flip the direction the motor is turning. The MMBe will always power up running
forward (MOTOR+ = VMOTOR, MOTOR- = GND during the positive duty cycle). REV toggles the
polarity of the voltage applied to the motor. In other words if the motor is running in reverse and the REV
command is sent it will start running forward. See also the new command SETDC_DIR where the motor
speed and direction are combined into a single command.
4.6 TACH Command
The MMBe monitors pulses at the TACH_IN pin on an ongoing basis. This measurement is accessed
with the TACH command. The optional GATETIME value may be appended to the command, or left off.
Tachometer measurements are updated every 125ms, and have a resolution of 8Hz. While you may
read the tachometer value more often than every 125ms, the actual value is not updated any faster than
that. Frequency measurements are factory calibrated to be within +/-0.5%(50Hz) or 10KHz, additional
calibration could be attempted using the READ_FREQCAL and WRITE_FREQCAL commands.
the TACH command is received the frequency of the signal at the TACH_IN pin is returned as 2 bytes,
with the high byte sent first. To actual frequency is FREQHI x 256 + FREQLO.
4.7 SETDC Command
SETDC is used to set the positive duty-cycle of the motor. This controls the motor speed. Duty-cycle is
expressed as a percentage of time ON (positive duty-cycle). The SPEED value is an 8-bit value, with 255
(0xFF) equaling 100% ON (full speed), and 0 (0x00) equaling 0% ON (not running). The duty-cycle also
relates to the average voltage across your motor. For example, in a 12V system a 50% duty-cycle would
equal and average voltage across the motor of 6V (50% at 12V + 50% at 0V). To send a 25% duty-cycle
you would send 25% of 255 (0xFF), or 64 (0x40).
When using the higher frequency mode (15.5KHz) you should expect less resolution in low speed control.
The turn on/off time for the H-bridge on the MMBe is too slow and swamps out the lower duty cycle
values. Therefore the H-bridge will not turn on unless the SPEED value is greater than 40 (15%).
Example of TACH Command with frequency of 10,000Hz (0x2710)
Example of SETDC Command with speed of 75% (191, or 0xBF)
Decimal
Decimal
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Hex
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Hex
Example of REV Command
Sync
0x55
Sync
0x55
85
85
FreqHi
Sync
0x55
0x27
85
39
Command
Command
0x02
0x03
2
3
Command
FreqLo
0x01
0x10
16
1
GateTime
(optional)
Speed
0x40
0xBF
191
64
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