The general purpose input/output (GPIO) board is an expansion board for MegaSquirt-II. It provides a number (up to 25) of additional inputs and outputs for MegaSquirt-II. The additional I/O lines are communicated over a CAN (controller area network) which allows communication between the GPIO and MegaSquirt-II. This allows there to be just two wires connecting the MegaSquirt-II and the GPIO, while still sending any number of I/O signals.

There's nothing electronically new on the GPIO board; the CPU, CAN, and clock circuits are straight from MegaSquirt-II, the power circuit is from the V3 main board, the serial circuit is from the V3 main board as well.

The 'features' of GPIO are:

• The GPIO board has the C64 processor and CAN (controller area network) chip, which are identical to those on MegaSquirt-II, and a separate serial connection (based on the V3 schematic),
  
• The GPIO board is designed so that more than one can be used. In fact, up to 15 CAN enabled boards (GPIO or router boards) can be used with MegaSquirt-II, giving a very large number of possibilities. All of the board can be controlled from MegaTune. A system with two GPIO and one router board might look like this:
  MegaTune/Laptop <--serial--> MS-II/MegaSquirt <--CAN--> GPIO <--CAN--> Router <--CAN--> GPIO

  where MegaTune is connected to the network over the one serial line, and the main board receives and relays messages over CAN and back to MegaTune.

• There are 3 types of input circuits and 3 types of output circuits. These are:
  • Inputs
    1. 5 general purpose inputs [GPIx], which can have voltage or resistance input, depending on build-time options (based on the V3 sensor input circuits), these can also be used for software debounced on/off switches,
    2. 4 VR inputs [VRx] (based on Bruce's EasyVR schematic), for things like transmission controller, vehicle speed indications, or traction control,
    3. 4 EGT circuits [EGTx] (using AD595 chips), for independent exhaust gas temperature measurements. (These can also be configured for resistance or voltage measurements, similar to the GPIx circuits)

  • Outputs
    1. 4 general purpose outputs [GPOx] (which have user selected 5V or 12V pull-ups, flyback, and LED capabilities),
    2. 4 PWM outputs [PWMx] (based on the uprated V3 PWM FIdle TIP120 circuit),
    3. 4 high current circuits [VBx], using the VB921 ignition module driver.

• The input and output circuits are 'modular', and each is be confined to an area of the PCB designated with a silkscreen box,
• Any of the I/O circuits can be used for direct port access (such as switch input - debounce in software - or for things like ignition module control (with provisions for a current limiting resistor),
• The 35 pin AMPSEAL weatherproof connector is used.
• The serial connection is via a stereo jack (or optionally it can be jumpered to the AMPSEAL connector).
• There is proto board access to dedicated 12V, 5V and ground on two 0.100" headers.
• There is an optional 'power on' LED indicator.
• The GPIO 4-layer (two signal planes sandwiching ground and power planes) board is a mix of surface mount devices (SMD) and regular components to maximize the build time options.
• The GPIO board is 4.00" by 6.00" (101.6mm x 152.4mm) in size, the same as the MegaSquirt^® main boards. It is designed to go into the same specification case as MegaSquirt.

The GPIO setup scheme is designed to be extremely flexible. There will be an easy to use compiler to set the GPIO configuration, allowing the user to set things like port PWM, frequency measurement, map inputs to functions or tables, and all the outputs with a number of arbitrary conditions and functions that can be linked together to form very complex relationships, if needed. The current plan is to make it work like EasyTherm, generate a modified .S19 file with this code embedded in it, and spit out a customized .INI file at the same time. Below is an example nitrous controller, but you'll get the general idea, the transmission controller software ("MegaShift") will be more complex but similarly structured.

//------------------------------------------------------------------------------ INTERFACE [Menu] menuDialog = main menu = "&Settings" subMenu = nitrousControl, "&Nitrous Control" [UserDefined] dialog = nitrousControl, "Nitrous Control" topicHelp = "http://www.mysite.com/nitrous.html" field = "Lower RPM Limit", nc.rpmLimit field = "RPM Hysteresis", nc.rpmHysteresis field = "Low Coolant Threshold", nc.lowerCoolantThreshold field = "Coolant Hysteresis", nc.lowerCoolantHysteresis field = "Throttle Threshold", nc.throttleEnable field = "Throttle Hysteresis", nc.throttleHysteresis END_INTERFACE //------------------------------------------------------------------------------ tpsADC = PORT( 3, ADC); nitrousEnable = PORT(12, OUTPUT, OFF); // Output to solenoid armSwitch = PORT(18, INPUT); // Toggle switch on dash #define MS2 0x01 #define GPIO 0x02 rpm = CAN(1, MS2, 4); clt = CAN(1, MS2, 8); tps = (tpsADC-124) * 100 / 893; // Hard coded TPS calibration for example. //------------------------------------------------------------------------------ BLOCK nc rpmLimit = CONST(3500, "rpm", 1.0, 0.0, 0, 8000, 0); rpmHysteresis = CONST( 100, "rpm", 1.0, 0.0, 0, 1000, 0); lowerCoolantThreshold = CONST( 150, "°F", 1.0, 0.0, 0, 300, 0); lowerCoolantHysteresis = CONST( 5, "°", 1.0, 0.0, 0, 30, 0); throttleEnable = CONST( 75, "%tps", 0.1, 0.0, 0, 100.0, 0); throttleHysteresis = CONST( 10, "%tps", 0.1, 0.0, 0, 10.0, 0); nitrousCond1 = rpm >= rpmLimit : rpmHysteresis; nitrousCond2 = tps > throttleEnable : throttleHysteresis; nitrousCond3 = clt > lowerCoolantThreshold : lowerCoolantHysteresis; nitrousEnable = armSwitch && nitrousCond1 && nitrousCond2 && nitrousCond3; END_BLOCK //------------------------------------------------------------------------------

For off-the-shelf control, we hope to stock a number of 'pre-built' config files (4L60E/4L80E, for example) and code so that people don't have to invent them.

The serial connector is NOT the primary connection to the system, most communications (everything other than re-flash) will typically be done over CAN to the main board, including configuration and datalogging.

Unlike MegaSquirt^® EFI Controller, the GPIO Board does not use a DB9 connector for serial communications. Instead it uses a 2.5 mm (aka. 3/32") sub-miniature stereo jack, of the same spec used for the Innovate LC-1 wide band controller:

This was done because the serial connection is used much less frequently with the GPIO board than with MegaSquirt^® EFI Controller, and it allows the serial connection to be sealed. (Optionally, the serial connections can be brought out through the AMPSEAL connector.)