Data Sheet

Status register

Bit 7 (msb) 6 5 4 3 2 1 Bit 0 (lsb)

Busy - - - -

over-temperature

limiter

over-current

limiter

Acceleration

in progress

Bit 0 is read as high when the drive is accelerating the motor. It will be cleared when the requested

speed is achieved or the over current or over temperature limiters are active.

Bit 1 set high indicates that the current through the motor has reached 20Amps and is being limited to

that value, the red LED will be illuminated when this happens.

Bit 2 set high indicates that the over temperature limiter is active. Above a preset threshold, the motor

current will be reduced in proportion to the MD04 temperature. The module can still be used but the

motor power will be limited, the red LED will be illuminated when this happens. It should be noted that

a few minutes of running continuously at 20A will cause the heatsink to get hot - watch your fingers!

Bit 7 is the busy flag. It is set high when you issue a new command to the module. It is cleared very

quickly and you are unlikely ever to see it set.

Speed register

Sets the maximum speed that the motor will accelerate to. It is actually the 8-bit value sent to the

modules PWM controller. Write a value of 0 to 243 (numbers from 243 to 255 are clamped to 243) .

The larger the number, the more power is applied to the motor.

Acceleration register

This sets the rate at which the motor accelerates or decelerates from where it is towards the new speed

set by the speed register. Write a value of 0 to 255, the larger the number the longer the module will

take to reach the new speed. Writing zero to the acceleration register will allow maximum acceleration

of 0 to full in 0.187 seconds. This value actually controls a timer which steps the current motor speed

towards the requested motor speed. It does this every (((acceleration register)*125)+768)uS. A value of

zero gives 768uS/step or 243*768=186624uS (0.187s) to accelerate from 0 to full. A value of 255 is

((255*125)+768)*243=7932249uS or just under 8 seconds.

Temperature register

Motor current

This is the value used internally to limit the motor current to 20A. You do not need to read or do

anything with it. The value is proportional to motor current, with a value of 186 representing the 20A

limit.

Software revision number

The revision number of the software in the modules PIC controller.