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Jaguar Detailed IO and Connection Specifications 
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This applies to 0.4-alpha and probably 0.6-alpha variants. Others could vary in subtle ways.


The Jaguar unit, and FreeEMS in general, are very very customisable and configurable. Thus this spec sheet reads a bit differently from the normal and is more complex. That's an unfortunate side effect of your freedom to do whatever the **** you want :-) In a commercial ECU more things would be nailed down more specifically and the spec sheet would thus be clearer, but your options more limited.


Total of 9 exposed analogue input pins (3 temperature, 6 linear). All re-purpose-able with config or code change (for core inputs).

  • 2 robust (voltage clamped) dedicated RPM/Position inputs (configurable VR/reluctor (semi-differential pair (4 pins)) or Hall/Optical (single-ended))
  • MAP on board 250kPa (or other to your taste) (or external to save cost if you prefer) (protection optional for external use only)
  • AAP (Barometer) on board (optional to install) (no protection to use external safely, but still possible)
  • Independent Battery Reference Voltage (BRV) sensing input for accuracy, fully protected from over/under/reverse voltage
  • IAT (Inlet Air Temperature) sensor input, fully protected from over/under/reverse voltage
  • CHT (Coolant/Head Temperature) sensor input, fully protected from over/under/reverse voltage
  • Spare temperature sensor input, fully protected from over/under/reverse voltage
  • TPS (Throttle Position Sensor) input, fully protected from over/under/reverse voltage
  • EGO (Exhaust Gas Oxygen) sensor input, fully protected from over/under/reverse voltage
  • MAF (Manifold Air Flow) sensor input, fully protected from over/under/reverse voltage
  • Firmware update logic input/jumper/switch/button (unprotected)
  • Up to 24 unprotected logic level IO pins, minus those used to control below drivers, as outputs, or digitally. (0-5V ONLY through current limit resistor)


  • 1 Dedicated fully-protected overkill fuel-pump relay low-side driver with indicator LED (up to 6A)
  • 2 General-purpose fully-protected low-current low-side drivers with indicator LEDs (PWM or on/off) (up to 6A)
  • 8 Robust fully-protected high-impedance injector drivers with indicator LEDs (or GP low-side drivers) (up to 6A or approximately 3 injectors per channel max)
  • 4 Robust (self limited) low-current ignitor drivers (drives ignitors, not coils) (can be used for LEDs or other things if not used for ignition) (2 are connected to pins, 2 are hw configurable)
  • 1 Logic-level unprotected CEL output with indicator LED (useful for light-duty LED drive ONLY, 1 LED only)
  • Up to 24 unprotected logic level IO pins, minus those used to control above drivers, as inputs, or digitally. (<= 20mA through current limit resistor)


  • 1 fully isolated (OK to use laptop with cheap inverter) high-speed USB connection for tuning and logging
  • 2 pins brought out for second UART use (eg in-car logging in another box) (if not used for inputs or outputs)
  • 2 pins brought out for CAN (Controller Area Network) module (if not used for inputs or outputs)

Other Connections

  • 2 Reference ground input connection points (CPU, regulators, analogue inputs)
  • 2 Dedicated and thermally fused 5V outputs for sensors (TPS, external MAP, etc) up to 1A max in total, 500mA max each
  • 1 Shared ground input for fuel pump and low-current low-side drivers
  • 8 (4 pairs) of Semi-shared ground inputs for injector drivers
  • 1 12V supply voltage input for regulators (transient and reverse-polarity protected)
  • 1 12v supply voltage input for output LEDs (not protected)
  • 3 sensor ground output connection points
  • 2 sensor ground shield connection points (for RPM inputs)


1) Only 6 injector XOR ignitor outputs, total on vanilla firmware. Shared between ignition and injection, eg 3/3, 4/2, 5/1, 6/0 as required. viewtopic.php?f=54&t=1084

2) If you use Sean's XGATE stuff you can obtain more injector channels but you get no support from me at all, and it's not well integrated yet so you may struggle and won't get critical (or any) updates or new features in a timely fashion unless your Git foo is strong.

3) Typical setup will only have 20 pins (of which 8 are PWM capable, 2 are UART, 2 are CAN) available for GP inputs and outputs, 4 having been used for above injector/ignition channels. 2 more are "hard coded" as ignition outputs.

4) Jaguar does NOT have a connector and must be wired to some type of connector or directly to a loom (yuck, don't do this). This is a pro for OEM case installations, and not difficult to achieve with other connectors either. VERY flexible which is nice. A bit manual, which is not so nice. It is what it is, and I love it. Connector requirements:

23 inputs and grounds and 5V supplies
15 outputs and
10 gnd/12v supplies for outputs and LEDs
2 parallel 12v supply pins for CPU/vregs
2 parallel gnd supply pins for CPU/vregs/sensors

Thus an ideal connector would have 52 pins, or more for logic inputs/ouputs/CAN/extra UART/etc which aren't included above. However less can be used if not all functionality is required. Some grounds and 12v and 5v points can also be combined intelligently to save pins.

I hope that this has been helpful to you! :-) Let me know if anything is wrong or missing!


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Thu Jul 25, 2013 12:15 pm
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Joined: Mon Feb 06, 2012 8:59 am
Posts: 9
Looks pretty good.


Thu Jul 25, 2013 12:52 pm
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