3.4 Communications lines 3 MS3PRO HARDWARE
3.3.3 High current outputs
These are ground switched outputs with a maximum current of 5 amps, just like the injector output channels (in
fact, it’s the same transistor type). These can be run in an on/off fashion or use pulse width modulation. Maximum
frequency is 1021 Hz. Flyback voltage spikes are clamped at 36 volts to help the valve close rapidly. They typically
work well with boost control solenoids and nitrous solenoids, which cycle fully off and fully on.
3.3.4 PWM medium current outputs
These are ground switched outputs, maximum current 3 amps. They are optimized for valves which use pulse width
modulation to hold them in an intermediate position instead of pulsing on and off. Flyback spikes are clamped at
battery voltage, which causes the valve to close more slowly. Common valves that would use these outputs include
idle air control valves and variable valve timing oil control valves. They can also be used as an on/off signal. The
fuel pump uses a similar circuit, although it does not use PWM. Maximum frequency on these outputs is 1021 Hz.
Note: Any device connected to these outputs must be set up so that it is powered off when the ECU is shut
down. Relays or solenoids connected to these outputs can back feed power into the MS3Pro if the relay coil or
solenoid winding receives power with the key on. Wire any device connected to these outputs to switched 12 volt
power.
3.3.5 Tach output
This output can be used to produce a 12 volt square wave signal. It can also trigger certain ignition modules such
as an MSD 6AL or a Ford TFI, or be used as a general purpose on/off output. When used as an on/off output, it
can sink up to 1 amp.
3.3.6 Stepper motor control output
The MS3Pro includes one stepper control output, with a maximum current of 750 mA per channel to drive a stepper
idle air control valve. However, its outputs can also be used as a tach signal or two general purpose on/off outputs.
When used as an on/off output, the device can be treated as two separate paired low / high side drivers. The A
output of either side will supply 12 volts is turned on, while the B output will supply ground a relay or solenoid.
Turning the output off reverses the pattern if the other output is on. If both outputs are off, all four outputs will not
supply any voltage or ground.
3.4 Communications lines
3.4.1 RS232
RS232 is an industrial strength serial connection. This is brought out to a 4 piece Weather Pack connector in the
harness, which connects to a cable that plugs into a 9 pin serial port on a laptop. RS232 is more noise resistant
than USB, and we recommend using this connection if your laptop supports this. Do not attempt to plug the RS232
connection into any sort of 15 or 25 pin connector - these are usually for VGA displays or joysticks. Some third
party devices such as Bluetooth adapters also use the RS232 connection.
3.4.2 USB
The MS3Pro features one USB output channel that allows it to communicate with a laptop. We recommend using
a shielded cable for best results as not all USB cables have full shielding.
3.4.3 CANbus
The CANbus wires are an automotive network that allow the MS3Pro to communicate with other CAN enabled
modules. Note that not all CAN enabled devices will communicate with the MS3Pro; CAN is a type of hardware,
and in addition to having the required hardware, the device you are attempting to connect to the MS3Pro must also
be programmed to understand the type of messages the MS3Pro sends. Devices currently or soon on the market
that can be connected to the MS3Pro include:
AMP EFI MS3Pro manual version 1.202, firmware 1.5.0, 4/21/2017 Page 27
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