ADC - stands for "analog-digital converter". In this case, it is part of the conversion circuitry in the CPU that translates the varying voltage signal to a digital value that the CPU can understand and operate on. All of the sensors (TPS, MAP, CLT, IAT) send their signal to a particular ADC on the processor. The ADC result is used by the processor as a 'count'. MS-I has an eight bit ADC, so the counts can be from 0 to 255. MS-II has a more precise 10-bit ADC, so the count can be from 0-1024. Both of these are mapped over a 0-5 Volt range (so the voltage into the ADC = ADC count * 5.0/1024 for MS-II, for example).
AE - Acceleration Enrichment, the enriched mixture provided when the throttle position sensor signal changes at various rates.
AFR - Air Fuel Ratio, the mass ratio of air to fuel in the combustion chamber. See NB- and WB-EGO sensors, below.
ASE - After Start Enrichment, the enriched mixture provided for a number of engine cycles when MegaSquirt® detects that the engine has transitioned from cranking to running.AMC - Automatic Mixture Control, the method MegaSquirt-II (V2.6+) uses to update the VE table in RAM and FLASH using feedback from the oxygen sensor. See the AMC page for more information.
ASE - After Start Enrichment, the enriched mixture provided when engine has just been started.
ATDC - After Top Dead Center, the crankshaft position with respect to the piston being at the top of its travel, meaning it has passed it's highest position and is descending.
BTDC - Before Top Dead Center, the crankshaft position with respect to the piston being at the top of its travel, meaning it has NOT passed it's highest position and is rising. Most normal spark event occur BTDC.
CAN - (Controller Area Network) - a dedicated automotive networking system to allow different automotive processor to communicate and share inputs and calculated results. Used for MegaSquirt-IITM and the GPIO board, router board, etc..
Carbon Monoxide (CO): in an automotive context, generally refers to regulated carbon monoxide (CO) tail pipe emissions. See: www.megamanual.com/ms2/tune.htm#emissions
Catalytic converter: a chemical device in the vehicle's exhaust system that can reduce the amount of regulated emissions emitted by converting NOx to N2 + 02, CO to CO2 and HC to CO2 + H20. Catalytic means the converter active substrate facilitates the reactions, but is not consumed (and thus has a long life with no replenishment requirements). See: www.megamanual.com/ms2/tune.htm#emissions
Closed loop - refers to those times when an EFI computer is using the feedback on the mixture provided by the oxygen sensor to effectively control the injected fuel amounts.
CHT - Cylinder Head Temperature, used instead of coolant temperature (CLT) on air-cooled engines.
CLT - CooLant Temperature sensor (aka. CTS). Usually the CLT sensor is an NTC (Negative Temperature Coefficient) thermistor, or a resistor whose resistance varies with temperature (NTC means the resistance goes down as the temperature goes up.
Compiler - a program used to generate other programs using a source code written in a computer language (assembly language, C, C++, etc.). People often use the term to refer to the program used to compile, link and locate to create a usable program. Example of Compilers are Microsoft's Visual Studio C++ .NET or Freescale's Codewarrior.
CPU - Central Processing Unit, aka. "processor" or "microprocessor" the computational engine that performs the calculations to operate the injection and ignition function in MegaSquirt®. It has a number of support circuits, like the power circuit, the clock circuit, the serial and CAN communications circuits, and various input and output conditioning circuits.
Cross-compiler - refers to a compiler (see) used on one platform (for example a Pentium processor running Windows OS) for use on another processor (MegaSquirt-IITM's HSC12 processor, for example).
CTS - Coolant Temperature Sensor (aka. CLT). Usually the CTS is an NTC (Negative Temperature Coefficient) thermistor, or a resistor whose resistance varies with temperature (NTC means the resistance goes down as the temperature goes up.
DMM (digital multi meter) electronic current/resistance/potential measuring tool.
DT (dual table) the dual table embedded code that has a number of additional features over the standard B&G embedded code.
Duty Cycle (DC)– A number indicating the amount of time that some signal is at full power. In the context of MegaSquirt® EFI Controller, duty cycle is used to describe the amount of time that the injectors are on, and to describe the “hold” part of the peak and hold injector drivers (see Low Impedance Injectors, below).
EasyTherm (ET) - A Windows program that simplifies configuring your MegaSquirt® to accept the substitution of non-standard temperature sensors and to upload software revisions.
ECU - (Electronic Control Unit) is the general term for a fuel injection controller, of which MegaSquirt® is an example.
EDIS - Electronic Distributorless Ignition System is Ford's wasted-spark computer-controlled ignition module, which has been made to work with modified versions of MegaSquirt®.
EGO Sensor - Exhaust Gas Oxygen sensor, used to describe the sensor in the exhaust that measures the lean/rich state of the intake mixture. Used to control the fuel via a feedback algorithm called “closed loop”.
EGT (Exhaust Gas Temperature) is the temperature of the exhaust gases, typically measured with a thermocouple (and a GPIO board - which has 4 dedicated EGT circuits).
FCCM: Acronym for field-programmable custom computing machine, a computing device in which programmable logic devices replace traditional general purpose processors, or fixed logic, in order to achieve superior performance or other capabilities.
FET (field effect transistor) - In MegaSquirt® EFI Controller, the transistors used to control the activation of the injectors.
FPGA: field-programmable gate array. This is a flexible, programmable switching network that will be used in UltraMegaSquirt.
FIdle - Fast Idle. A device used to control idle speed with additional air supplied by a vacuum solenoid. MegaSquirt has a simple on-off fast idle control, and does not have the ability to drive a PWM IAC (Idle Air Control) device.
Gamma - Used to indicate the change in a fuel amount from the calculated amount.
Gego - Gego is short for 'Gamma - Exhaust Gas Oxygen'. It is the change applied to the fuelling equation based on the EGO O2 sensor feedback. This feedback can (and is) done in a number of different ways, depending on the type of sensor, etc. The important thing is that this is a result of an external measurement, not a pure calculation, so it appears a bit mysteriously in the equation.
GPIO - (General Purpose Input/Output Board) - A CAN enabled processor equipped expansion board for MegaSquirt-II.
GM - General Motors, the manufacturer for the default coolant and air temperature sensors used with MegaSquirt®.
Hall sensor - an "active", magnetic field presence sensor. It is based on the Hall effect. The Hall effect is the change of resistance in a semiconductor in a magnetic field. The Hall effect sensor consists of semiconductor material which will conduct current when the material is subject to a magnetic field. These types of sensors require a "flying magnet", wheel. Instead of teeth on the wheel, as in a variable reluctor sensor, you must have small magnet and a shutter wheel.
Hydrocarbon (HC): in an automotive context, generally refers to regulated unburned hydrocarbon tail pipe emissions. See: www.megamanual.com/ms2/tune.htm#emissions
HEI - High Energy Ignition, the distributor based electronically controlled ignition system from General Motors. There are a number of variant, identified by the module they use:
High Impedance Injectors - (a.k.a. hi-Z) Fuel injectors designed to work with a simple switch in a 12 volt circuit, no special signal conditioning is required to drive them. The resistance of a high impedance injector is about 10-15 ohms.
HR - (high resolution) the high resolution embedded code that gives higher injector pulse width resolution than the standard B&G embedded code.
Hz (Hertz) the measurement of the frequency of a cyclical event, it represent to number of times per second the cycle is completed.
IAC - Idle Air Controller, though it term is sometimes used more generally, it usually refers to GM's stepper motor controller for additional idle air (and hence engine speed) during warm-up.
IAT sensor - Intake Air Temperature sensor, same as MAT, see below.
IGBT - Insulted Gate Bipolar Transistor a particular kind of transistor especially suitable for driving ignition coils.
kPa (kiloPascals) - the measurement of air pressure used in MegaSquirt® computations. It ranges from 0 (vacuum) to 101.3 kPa (standard atmospheric pressure at sea level) to 250 kPa (21psi of boost) or higher.
LIW: Acronym for long instruction word, an instruction set architecture which explicitly encodes several independent instructions, to be executed concurrently, in each "instruction word".
logic cell: A unit of FPGA "area" equivalent to one 4-input lookup table and one D flip-flop.
LUT: Acronym for lookup table. A small RAM (e.g. flip-flops with output multiplexer tree), usually 16 bits (sometimes 8 bits), that implements an arbitrary combinational logic function of 4 (respectively, 3) inputs. Often found with a number prefix that indicates precise number of inputs. Thus a 4-LUT is a 4-input (16 bit RAM) lookup table.
Low Impedance Injectors - (a.k.a low-Z) Fuel injectors that are designed to run at a much lower current than would be supplied by a direct 12 volt connection. They require a special signal that is initially at full current (4-6 amps, a.k.a. “peak current”) for about 1.0-1.5 ms, but then drops down to about 1 amp (“hold current”) for the rest of the opening pulse. The resistance of a low-impedance injector is typically 1-3 ohms.
LSU-4 - Bosch wide-band oxygen sensor, planned for use in the Precision Wideband Controller.
MAP sensor - Manifold Absolute Pressure sensor. Measure of the absolute pressure in the intake manifold (related to the engine vacuum), to determine the load on the engine and the consequent fueling requirements. The standard MAP sensor in MegaSquirt® is the MPX4250 (2.50 BAR, or 15 psi (vacuum) + 21 psig (boost)).
MAT Sensor - Manifold Air Temperature sensor, the same as IAT. The MAT circuit is identical to the CTS circuit, see CTS, above.
MIMD: Acronym for multiple instruction, multiple data. A parallel computer with multiple independent threads of control. Conventional symmetric multiprocessors are MIMD architectures.
MJL - MegaJolt Lite, used in this document to refer to the ignition supplement to the MegaSquirt® fuel injection controller.
MJLJr - MegaJolt Lite Junior, used in this document to refer to the ignition supplement to the MegaSquirt® fuel injection controller.
MPX4250AP - the internal MAP sensor used in MegaSquirt.
MT - MegaTune, Eric Fahlgren's Windows-based configuration program for the MegaSquirt® EFI controller.
MS - MegaSquirt, used in this document to refer to the MegaSquirt® fuel injection controller or its embedded software.
MSTweak3000 - a Windows program which will sort through your data logs and calculate VE points that need to be changed.
NB-EGO Sensor - Narrow Band EGO sensor, gives a switch at the stoichiometric ratio (the chemically correct mixture of air and fuel), but unreliable for AFR other than stoichiometric.
Oxides of Nitrogen (NOx): in an automotive context, generally refers to regulated 'mono-nitrogen oxides' (NO and NO2) tail pipe emissions. See: www.megamanual.com/ms2/tune.htm#emissions
OEM (original equipment manufacturer) - refers to parts produced for initial assembly of a new vehicle.
Open Loop - refers to those times when MegaSquirt® ignores the feedback from the oxygen sensor.
PCB (printed circuit board) - the fibreglass board that has the MegaSquirt® component layout and circuits imprinted on it.
PC Configurator (PCC) - The original tuning software from Bowling and Grippo, it has fewer features than MegaTune, and doesn't work with MSnS-E or MegaSquirt-II.
Pull up a very simple circuit consisting of a voltage supply and a current limiting resistor designed to prevent a signal from floating, it forces the signal to either be high (equal to the pull up voltage) or low (grounded).
PW (Pulse Width) is the amount of time a signal is applied during each period. For example, is the amount of time (in milliseconds) an injector is pulled low (grounded) to inject fuel.
P&H Injectors - Peak and hold injectors; see Low Impedance injectors.
PIP - Profile Ignition Pick-up is the term used for the signal sent from Ford's Electronic Distributorless Ignition System (EDIS) to the electronic control unit. This is a digitally modified alternating current (AC) signal that originates from a crank angle sensor. The PIP signal into the ECU is a square wave switched at 12 volts. It provides information about both the engine speed and position.
Pulse Width Modulation (PWM) - A signal with a fixed pulse width (frequency), which is turned on for part of the pulse. The percent of time that the signal is on is called its duty cycle. PWM is used to control voltage (and consequently current) to fuel injectors.
Required Fuel – (Req_Fuel) The injector pulse width, in milliseconds, required to supply the fuel for a single injection event at stoichiometric combustion, 100% volumetric efficiency and standard temperature.
Router Board - The router board is a add-on circuit board for MegaSquirt-II which converts the MegaSquirt-II batch injection pulse to a sequential setup, then 'routes' this pulse to specific injectors based on the instantaneous crank angle (this requires a crank wheel and cam sync).
RPM: In FPGA, an acronym for relatively placed macro. Xilinx specific. A group of device primitives to which RLOC= attributes have been applied, in order to constrain the placement of the group and thereby floorplan the group. For example, attributing a with RLOC=R0C0, b with RLOC=R0C0 and c with RLOC=R0C1 constrains a and b to be placed in the same CLB/slice and c to be placed in the adjacent slice in the next column. Wherever a, b, and c may be placed in the device, they'll be placed together.
SAW - Spark Advance Word is the 'returning' signal to a Ford EDIS ignition unit from the ECU that sets the amount of ignition advance requested. It is in the form of a 5 volt square wave.
SIMD: Acronym for single instruction, multiple data. A parallel computer with a single thread of control broadcast across the plurality of execution units. Example: Thinking Machines CM-1.
SoC: Acronym for system-on-a-chip, an integrated embedded computer system on a single chip. In the context of SRAM-based FPGAs, this usually discounts an external FPGA configuration ROM and external RAM.
Stim (MegaStimulator) - the Stimulator is a small board which plugs into the connector of the MegaSquirt. It simulates all the sensor the inputs the MegaSquirt® would normally see and provides power to the MegaSquirt. The Stimulator also allows you to monitor the MegaSquirt's injection pulses [actual], fuel pump relay operation, and fast idle solenoid output with four LEDs.
SPOUT - Spark Out is the spark advance signal sent from MS-II/MSnS-E to the Ford TFI module to set the timing advance.
TBI - Throttle Body Injection is a form of injection is which the fuel is injected above the throttle(s). It was typically used on older engines since it can be a simpler system, but is also found on some very high output racing engines because the vaporization time is longer than with port injection.
TPI - Tuned Port Injection is General Motors bank-fire port fuel injection system. It was widely used on 305 and 350 cid V8 in the mid to late 1980's.
TPS - Throttle Position Sensor, a voltage divider that gives information to MS about throttle opening, from which it computes rate of throttle opening for acceleration enrichment.
Volatile Organic Compounds (VOC): in an automotive context, generally refers to organic components or precursors to smog formation. Organic compounds are all chemical compounds containing carbon-hydrogen (C-H) bonds of covalent character. The U.S. Environmental Protection Agency defines a VOC as any organic compound that participates in a photoreaction. An example of a VOC is PAN (peroxyacetyl nitrate), CH3COOONO2. See: www.megamanual.com/ms2/tune.htm#emissions
VB921 - a particular IGBT designed for use with automotive ignition coils, it is used with the V3 main board, for example.
VE - Volumetric Efficiency. The actual amount of air being pumped by the engine as compared to its theoretical maximum. A 200 cubic inch motor will theoretically move 200 cubic inches of air in one cycle at 100% efficiency. If the engine is actually running at 75% VE, then it will move 150 cubic inches of air on each cycle.
Vref - a 5 Volt supply used to power the TPS sensor (and sometimes other external components needing a 5 Volt supply, like ignition modules or pull-ups).
VR sensor - variable reluctor sensor is an induction type sensor, it is "passive", i.e. it does not require a power source, and has a small magnet built in.
Wasted Spark - A method of firing spark plugs in which one 'double-ended' coil simultaneously fires two coils on different cylinders. One of the cylinders is the intended 'target', and is near TDC on its compression stroke, the other cylinder is offset by 360° in the firing order (of the 720° 4-stroke cycle), so it is near TDC on its exhaust stroke. The second spark is said to be 'wasted' because it does not ignite a mixture. On the other hand, the hot ionized exhaust gases require little energy to create a spark, so nearly all the energy goes to the 'target' cylinder. An example of a wasted spark system, is Ford's EDIS. The advantage is that while a missing tooth crank wheel is required, no cam sync signal (and the corresponding wheel and sensor) are needed.
WB-EGO Sensor - Wide Band EGO sensor, can be used to derive real AFR data with mixtures from 10:1 to 20:1, i.e. anything you are likely to be interested in.
WOT - Wide open throttle.
WUE - Warm Up Enrichment, the enriched mixture applied when the coolant temperature is low.