27961 Parallax Inc, 27961 Datasheet - Page 16

• 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
4.15 READ_COUNTER Command
This command allows you to read the raw counter value used with the COUNT command. It may be
useful in determining the exact number of pulses received at the TACH_IN pin during a COUNT. Keep in
mind that the COUNT command will stop driving a motor after it has received a set number of pulses, but
the motor’s inertia will continue to spin it for a short period. This overshoot can be read using the
READ_COUNTER command.
4.16 CHANGE_BAUD Command
The MMBe is factory programmed for 2.4KBPS serial communication. But you can increase the rate of
communication to 9.6KBPS. The CHANGE_BAUD command toggles between these two settings, and
stores the most recent setting in EEPROM. You only need to make this change one time. Whatever
baud rate you set the device for will become the default baud rate. The change in baud rate takes place
upon reception of this command.
4.17 CHANGE_FREQ Command
The old MMB had a software generated PWM frequency of 61Hz. Yep, we know this is slow, but it was
designed for driving hobby robot platforms, and 61Hz noise was much more palatable than the whine of a
1KHz PWM signal. Since increasing the PWM frequency changes the efficiency of the motor drive circuit,
we tried hard to provide a PWM frequency that was similarly slow as the default frequency for the MMBe.
This way customers switching from the older products would be less likely to see noticeable changes in
motor speed between the two versions of the product.
But, we also recognized that backwards compatibility should not prevent us from using a higher PWM
frequency above the audible level. So the default PWM frequency is 15.5KHz, but the frequency may be
changed to a lower 242Hz with the CHANGE_FREQ command. This command toggles between the two
available PWM frequencies and stores the new setting in EEPROM (as the power up default setting).
You can read the STATUS.FREQLOW bit to see which frequency you are using.
Oddly enough the H-bridge used on the MMBe is designed to operate in the audible range (1-2KHz). So
operating at 15.5Khz will provide less resolution at the lower end of duty cycles. The H-bridge will not
turn on unless the duty cycle is greater than 40 (15%) due to the turn-on/off times of the H-bridge. For a
lot of motors this is not a serious issue. But if you need that low-end resolution you can always return to
the “old-school” frequency (242Hz).
Example READ_COUNTER returning a count of 10,000
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Decimal
Decimal
Decimal
Decimal
Send
Receive
Send
Send
Hex
Hex
Hex
CHANGE_BAUD Command
CHANGE_FREQ Command
CountHi
Sync
Sync
Sync
0x55
0x55
85
85
85
0x27
39
Command
Command
Command
CountLO
0x0B
0x0D
0x10
11
12
13
16
Solutions Cubed
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