An I/O controller for virtual pinball machines: accelerometer nudge sensing, analog plunger input, button input encoding, LedWiz compatible output controls, and more.

Dependencies:   mbed FastIO FastPWM USBDevice

Fork of Pinscape_Controller by Mike R


This is Version 2 of the Pinscape Controller, an I/O controller for virtual pinball machines. (You can find the old version 1 software here.) Pinscape is software for the KL25Z that turns the board into a full-featured I/O controller for virtual pinball, with support for accelerometer-based nudging, a real plunger, button inputs, and feedback device control.

In case you haven't heard of the concept before, a "virtual pinball machine" is basically a video pinball simulator that's built into a real pinball machine body. A TV monitor goes in place of the pinball playfield, and a second TV goes in the backbox to serve as the "backglass" display. A third smaller monitor can serve as the "DMD" (the Dot Matrix Display used for scoring on newer machines), or you can even install a real pinball plasma DMD. A computer is hidden inside the cabinet, running pinball emulation software that displays a life-sized playfield on the main TV. The cabinet has all of the usual buttons, too, so it not only looks like the real thing, but plays like it too. That's a picture of my own machine to the right. On the outside, it's built exactly like a real arcade pinball machine, with the same overall dimensions and all of the standard pinball cabinet hardware.

A few small companies build and sell complete, finished virtual pinball machines, but I think it's more fun as a DIY project. If you have some basic wood-working skills and know your way around PCs, you can build one from scratch. The computer part is just an ordinary Windows PC, and all of the pinball emulation can be built out of free, open-source software. In that spirit, the Pinscape Controller is an open-source software/hardware project that offers a no-compromises, all-in-one control center for all of the unique input/output needs of a virtual pinball cabinet. If you've been thinking about building one of these, but you're not sure how to connect a plunger, flipper buttons, lights, nudge sensor, and whatever else you can think of, this project might be just what you're looking for.

You can find much more information about DIY Pin Cab building in general in the Virtual Cabinet Forum on Also visit my Pinscape Resources page for more about this project and other virtual pinball projects I'm working on.


  • Pinscape Release Builds: This page has download links for all of the Pinscape software. To get started, install and run the Pinscape Config Tool on your Windows computer. It will lead you through the steps for installing the Pinscape firmware on the KL25Z.
  • Config Tool Source Code. The complete C# source code for the config tool. You don't need this to run the tool, but it's available if you want to customize anything or see how it works inside.


The new Version 2 Build Guide is now complete! This new version aims to be a complete guide to building a virtual pinball machine, including not only the Pinscape elements but all of the basics, from sourcing parts to building all of the hardware.

You can also refer to the original Hardware Build Guide (PDF), but that's out of date now, since it refers to the old version 1 software, which was rather different (especially when it comes to configuration).

System Requirements

The new config tool requires a fairly up-to-date Microsoft .NET installation. If you use Windows Update to keep your system current, you should be fine. A modern version of Internet Explorer (IE) is required, even if you don't use it as your main browser, because the config tool uses some system components that Microsoft packages into the IE install set. I test with IE11, so that's known to work. IE8 doesn't work. IE9 and 10 are unknown at this point.

The Windows requirements are only for the config tool. The firmware doesn't care about anything on the Windows side, so if you can make do without the config tool, you can use almost any Windows setup.

Main Features

Plunger: The Pinscape Controller started out as a "mechanical plunger" controller: a device for attaching a real pinball plunger to the video game software so that you could launch the ball the natural way. This is still, of course, a central feature of the project. The software supports several types of sensors: a high-resolution optical sensor (which works by essentially taking pictures of the plunger as it moves); a slide potentionmeter (which determines the position via the changing electrical resistance in the pot); a quadrature sensor (which counts bars printed on a special guide rail that it moves along); and an IR distance sensor (which determines the position by sending pulses of light at the plunger and measuring the round-trip travel time). The Build Guide explains how to set up each type of sensor.

Nudging: The KL25Z (the little microcontroller that the software runs on) has a built-in accelerometer. The Pinscape software uses it to sense when you nudge the cabinet, and feeds the acceleration data to the pinball software on the PC. This turns physical nudges into virtual English on the ball. The accelerometer is quite sensitive and accurate, so we can measure the difference between little bumps and hard shoves, and everything in between. The result is natural and immersive.

Buttons: You can wire real pinball buttons to the KL25Z, and the software will translate the buttons into PC input. You have the option to map each button to a keyboard key or joystick button. You can wire up your flipper buttons, Magna Save buttons, Start button, coin slots, operator buttons, and whatever else you need.

Feedback devices: You can also attach "feedback devices" to the KL25Z. Feedback devices are things that create tactile, sound, and lighting effects in sync with the game action. The most popular PC pinball emulators know how to address a wide variety of these devices, and know how to match them to on-screen action in each virtual table. You just need an I/O controller that translates commands from the PC into electrical signals that turn the devices on and off. The Pinscape Controller can do that for you.

Expansion Boards

There are two main ways to run the Pinscape Controller: standalone, or using the "expansion boards".

In the basic standalone setup, you just need the KL25Z, plus whatever buttons, sensors, and feedback devices you want to attach to it. This mode lets you take advantage of everything the software can do, but for some features, you'll have to build some ad hoc external circuitry to interface external devices with the KL25Z. The Build Guide has detailed plans for exactly what you need to build.

The other option is the Pinscape Expansion Boards. The expansion boards are a companion project, which is also totally free and open-source, that provides Printed Circuit Board (PCB) layouts that are designed specifically to work with the Pinscape software. The PCB designs are in the widely used EAGLE format, which many PCB manufacturers can turn directly into physical boards for you. The expansion boards organize all of the external connections more neatly than on the standalone KL25Z, and they add all of the interface circuitry needed for all of the advanced software functions. The big thing they bring to the table is lots of high-power outputs. The boards provide a modular system that lets you add boards to add more outputs. If you opt for the basic core setup, you'll have enough outputs for all of the toys in a really well-equipped cabinet. If your ambitions go beyond merely well-equipped and run to the ridiculously extravagant, just add an extra board or two. The modular design also means that you can add to the system over time.

Expansion Board project page

Update notes

If you have a Pinscape V1 setup already installed, you should be able to switch to the new version pretty seamlessly. There are just a couple of things to be aware of.

First, the "configuration" procedure is completely different in the new version. Way better and way easier, but it's not what you're used to from V1. In V1, you had to edit the project source code and compile your own custom version of the program. No more! With V2, you simply install the standard, pre-compiled .bin file, and select options using the Pinscape Config Tool on Windows.

Second, if you're using the TSL1410R optical sensor for your plunger, there's a chance you'll need to boost your light source's brightness a little bit. The "shutter speed" is faster in this version, which means that it doesn't spend as much time collecting light per frame as before. The software actually does "auto exposure" adaptation on every frame, so the increased shutter speed really shouldn't bother it, but it does require a certain minimum level of contrast, which requires a certain minimal level of lighting. Check the plunger viewer in the setup tool if you have any problems; if the image looks totally dark, try increasing the light level to see if that helps.

New Features

V2 has numerous new features. Here are some of the highlights...

Dynamic configuration: as explained above, configuration is now handled through the Config Tool on Windows. It's no longer necessary to edit the source code or compile your own modified binary.

Improved plunger sensing: the software now reads the TSL1410R optical sensor about 15x faster than it did before. This allows reading the sensor at full resolution (400dpi), about 400 times per second. The faster frame rate makes a big difference in how accurately we can read the plunger position during the fast motion of a release, which allows for more precise position sensing and faster response. The differences aren't dramatic, since the sensing was already pretty good even with the slower V1 scan rate, but you might notice a little better precision in tricky skill shots.

Keyboard keys: button inputs can now be mapped to keyboard keys. The joystick button option is still available as well, of course. Keyboard keys have the advantage of being closer to universal for PC pinball software: some pinball software can be set up to take joystick input, but nearly all PC pinball emulators can take keyboard input, and nearly all of them use the same key mappings.

Local shift button: one physical button can be designed as the local shift button. This works like a Shift button on a keyboard, but with cabinet buttons. It allows each physical button on the cabinet to have two PC keys assigned, one normal and one shifted. Hold down the local shift button, then press another key, and the other key's shifted key mapping is sent to the PC. The shift button can have a regular key mapping of its own as well, so it can do double duty. The shift feature lets you access more functions without cluttering your cabinet with extra buttons. It's especially nice for less frequently used functions like adjusting the volume or activating night mode.

Night mode: the output controller has a new "night mode" option, which lets you turn off all of your noisy devices with a single button, switch, or PC command. You can designate individual ports as noisy or not. Night mode only disables the noisemakers, so you still get the benefit of your flashers, button lights, and other quiet devices. This lets you play late into the night without disturbing your housemates or neighbors.

Gamma correction: you can designate individual output ports for gamma correction. This adjusts the intensity level of an output to make it match the way the human eye perceives brightness, so that fades and color mixes look more natural in lighting devices. You can apply this to individual ports, so that it only affects ports that actually have lights of some kind attached.

IR Remote Control: the controller software can transmit and/or receive IR remote control commands if you attach appropriate parts (an IR LED to send, an IR sensor chip to receive). This can be used to turn on your TV(s) when the system powers on, if they don't turn on automatically, and for any other functions you can think of requiring IR send/receive capabilities. You can assign IR commands to cabinet buttons, so that pressing a button on your cabinet sends a remote control command from the attached IR LED, and you can have the controller generate virtual key presses on your PC in response to received IR commands. If you have the IR sensor attached, the system can use it to learn commands from your existing remotes.

Yet more USB fixes: I've been gradually finding and fixing USB bugs in the mbed library for months now. This version has all of the fixes of the last couple of releases, of course, plus some new ones. It also has a new "last resort" feature, since there always seems to be "just one more" USB bug. The last resort is that you can tell the device to automatically reboot itself if it loses the USB connection and can't restore it within a given time limit.

More Downloads

  • Custom VP builds: I created modified versions of Visual Pinball 9.9 and Physmod5 that you might want to use in combination with this controller. The modified versions have special handling for plunger calibration specific to the Pinscape Controller, as well as some enhancements to the nudge physics. If you're not using the plunger, you might still want it for the nudge improvements. The modified version also works with any other input controller, so you can get the enhanced nudging effects even if you're using a different plunger/nudge kit. The big change in the modified versions is a "filter" for accelerometer input that's designed to make the response to cabinet nudges more realistic. It also makes the response more subdued than in the standard VP, so it's not to everyone's taste. The downloads include both the updated executables and the source code changes, in case you want to merge the changes into your own custom version(s).

    Note! These features are now standard in the official VP releases, so you don't need my custom builds if you're using 9.9.1 or later and/or VP 10. I don't think there's any reason to use my versions instead of the latest official ones, and in fact I'd encourage you to use the official releases since they're more up to date, but I'm leaving my builds available just in case. In the official versions, look for the checkbox "Enable Nudge Filter" in the Keys preferences dialog. My custom versions don't include that checkbox; they just enable the filter unconditionally.
  • Output circuit shopping list: This is a saved shopping cart at with the parts needed to build one copy of the high-power output circuit for the LedWiz emulator feature, for use with the standalone KL25Z (that is, without the expansion boards). The quantities in the cart are for one output channel, so if you want N outputs, simply multiply the quantities by the N, with one exception: you only need one ULN2803 transistor array chip for each eight output circuits. If you're using the expansion boards, you won't need any of this, since the boards provide their own high-power outputs.
  • Cary Owens' optical sensor housing: A 3D-printable design for a housing/mounting bracket for the optical plunger sensor, designed by Cary Owens. This makes it easy to mount the sensor.
  • Lemming77's potentiometer mounting bracket and shooter rod connecter: Sketchup designs for 3D-printable parts for mounting a slide potentiometer as the plunger sensor. These were designed for a particular slide potentiometer that used to be available from an seller but is no longer listed. You can probably use this design as a starting point for other similar devices; just check the dimensions before committing the design to plastic.

Copyright and License

The Pinscape firmware is copyright 2014, 2021 by Michael J Roberts. It's released under an MIT open-source license. See License.

Warning to VirtuaPin Kit Owners

This software isn't designed as a replacement for the VirtuaPin plunger kit's firmware. If you bought the VirtuaPin kit, I recommend that you don't install this software. The VirtuaPin kit uses the same KL25Z microcontroller that Pinscape uses, but the rest of its hardware is different and incompatible. In particular, the Pinscape firmware doesn't include support for the IR proximity sensor used in the VirtuaPin plunger kit, so you won't be able to use your plunger device with the Pinscape firmware. In addition, the VirtuaPin setup uses a different set of GPIO pins for the button inputs from the Pinscape defaults, so if you do install the Pinscape firmware, you'll have to go into the Config Tool and reassign all of the buttons to match the VirtuaPin wiring.


12 months ago

File content as of revision 109:310ac82cbbee:

// TLC59116 interface
// The TLC59116 is a 16-channel constant-current PWM controller chip with
// an I2C interface.
// Up to 14 of these chips can be connected to a single bus.  Each chip needs
// a unique address, configured via four pin inputs.  (The I2C address is 7
// bits, but the high-order 3 bits are fixed in the hardware, leaving 4 bits
// to configure per chip.  Two of the possible 16 addresses are reserved by
// the chip hardware as broadcast addresses, leaving room for 14 unique chip
// addresses per bus.)
// pull-ups in the KL25Z GPIO ports will only work if the bus speed is 
// limited to 100kHz.  Higher speeds require external pull-ups.  Because
// of the relatively high data rate required, we use the maximum 1MHz bus 
// speed, requiring external pull-ups.  These are typically 2.2K.
// This chip is similar to the TLC5940, but has a more modern design with 
// several advantages, including a standardized and much more robust data 
// interface (I2C) and glitch-free startup.  The only downside vs the TLC5940 
// is that it's only available in an SMD package, whereas the TLC5940 is 
// available in easy-to-solder DIP format.  The DIP 5940 is longer being 
// manufactured, but it's still easy to find old stock; when those run out,
// though, and the choice is between SMD 5940 and 59116, the 59116 will be
// the clear winner.

#ifndef _TLC59116_H_
#define _TLC59116_H_

#include "mbed.h"
#include "BitBangI2C.h"

// Which I2C class are we using?  We use this to switch between
// BitBangI2C and MbedI2C for testing and debugging.
#define I2C_Type BitBangI2C

// register constants
struct TLC59116R
    // control register bits
    static const uint8_t CTL_AIALL = 0x80;         // auto-increment mode, all registers
    static const uint8_t CTL_AIPWM = 0xA0;         // auto-increment mode, PWM registers only
    static const uint8_t CTL_AICTL = 0xC0;         // auto-increment mode, control registers only
    static const uint8_t CTL_AIPWMCTL = 0xE0;      // auto-increment mode, PWM + control registers only

    // register addresses
    static const uint8_t REG_MODE1 = 0x00;         // MODE1
    static const uint8_t REG_MODE2 = 0x01;         // MODE2
    static const uint8_t REG_PWM0 = 0x02;          // PWM 0
    static const uint8_t REG_PWM1 = 0x03;          // PWM 1
    static const uint8_t REG_PWM2 = 0x04;          // PWM 2
    static const uint8_t REG_PWM3 = 0x05;          // PWM 3
    static const uint8_t REG_PWM4 = 0x06;          // PWM 4
    static const uint8_t REG_PWM5 = 0x07;          // PWM 5
    static const uint8_t REG_PWM6 = 0x08;          // PWM 6
    static const uint8_t REG_PWM7 = 0x09;          // PWM 7
    static const uint8_t REG_PWM8 = 0x0A;          // PWM 8
    static const uint8_t REG_PWM9 = 0x0B;          // PWM 9
    static const uint8_t REG_PWM10 = 0x0C;         // PWM 10
    static const uint8_t REG_PWM11 = 0x0D;         // PWM 11
    static const uint8_t REG_PWM12 = 0x0E;         // PWM 12
    static const uint8_t REG_PWM13 = 0x0F;         // PWM 13
    static const uint8_t REG_PWM14 = 0x10;         // PWM 14
    static const uint8_t REG_PWM15 = 0x11;         // PWM 15
    static const uint8_t REG_GRPPWM = 0x12;        // Group PWM duty cycle
    static const uint8_t REG_GRPFREQ = 0x13;       // Group frequency register
    static const uint8_t REG_LEDOUT0 = 0x14;       // LED driver output status register 0
    static const uint8_t REG_LEDOUT1 = 0x15;       // LED driver output status register 1
    static const uint8_t REG_LEDOUT2 = 0x16;       // LED driver output status register 2
    static const uint8_t REG_LEDOUT3 = 0x17;       // LED driver output status register 3
    // MODE1 bits
    static const uint8_t MODE1_AI2 = 0x80;         // auto-increment mode enable
    static const uint8_t MODE1_AI1 = 0x40;         // auto-increment bit 1
    static const uint8_t MODE1_AI0 = 0x20;         // auto-increment bit 0
    static const uint8_t MODE1_OSCOFF = 0x10;      // oscillator off
    static const uint8_t MODE1_SUB1 = 0x08;        // subaddress 1 enable
    static const uint8_t MODE1_SUB2 = 0x04;        // subaddress 2 enable
    static const uint8_t MODE1_SUB3 = 0x02;        // subaddress 3 enable
    static const uint8_t MODE1_ALLCALL = 0x01;     // all-call enable
    // MODE2 bits
    static const uint8_t MODE2_EFCLR = 0x80;       // clear error status flag
    static const uint8_t MODE2_DMBLNK = 0x20;      // group blinking mode
    static const uint8_t MODE2_OCH = 0x08;         // outputs change on ACK (vs Stop command)
    // LEDOUTn states
    static const uint8_t LEDOUT_OFF = 0x00;        // driver is off
    static const uint8_t LEDOUT_ON = 0x01;         // fully on
    static const uint8_t LEDOUT_PWM = 0x02;        // individual PWM control via PWMn register
    static const uint8_t LEDOUT_GROUP = 0x03;      // PWM control + group dimming/blinking via PWMn + GRPPWM

// Individual unit object.  We create one of these for each unit we
// find on the bus.  This keeps track of the state of each output on
// a unit so that we can update outputs in batches, to reduce the 
// amount of time we spend in I2C communications during rapid updates.
struct TLC59116Unit
        // start inactive, since we haven't been initialized yet
        active = false;
        // set all brightness levels to 0 intially
        memset(bri, 0, sizeof(bri));
        // mark all outputs as dirty to force an update after initializing
        dirty = 0xFFFF;
    // initialize
    void init(int addr, I2C_Type &i2c)
        // set all output drivers to individual PWM control
        const uint8_t all_pwm = 
            | (TLC59116R::LEDOUT_PWM << 2)
            | (TLC59116R::LEDOUT_PWM << 4)
            | (TLC59116R::LEDOUT_PWM << 6);
        static const uint8_t buf[] = { 
            TLC59116R::REG_LEDOUT0 | TLC59116R::CTL_AIALL,
        int err = i2c.write(addr << 1, buf, sizeof(buf));

        // turn on the oscillator
        static const uint8_t buf2[] = { 
            TLC59116R::MODE1_AI2 | TLC59116R::MODE1_ALLCALL 
        err |= i2c.write(addr << 1, buf2, sizeof(buf));
        // mark the unit as active if the writes succeeded
        active = !err;
    // Set an output
    void set(int idx, int val)
        // validate the index
        if (idx >= 0 && idx <= 15)
            // record the new brightness
            bri[idx] = val;
            // set the dirty bit
            dirty |= 1 << idx;
    // Get an output's current value
    int get(int idx) const
        return idx >= 0 && idx <= 15 ? bri[idx] : -1;
    // Send I2C updates
    void send(int addr, I2C_Type &i2c)
        // Scan all outputs.  I2C sends are fairly expensive, so we
        // minimize the send time by using the auto-increment mode.
        // Optimizing this is a bit tricky.  Suppose that the outputs
        // are in this state, where c represents a clean output and D
        // represents a dirty output:
        //    cccDcDccc...
        // Clearly we want to start sending at the first dirty output
        // so that we don't waste time sending the three clean bytes
        // ahead of it.  However, do we send output[3] as one chunk
        // and then send output[5] as a separate chunk, or do we send
        // outputs [3],[4],[5] as a single block to take advantage of
        // the auto-increment mode?  Based on I2C bus timing parameters,
        // the answer is that it's cheaper to send this as a single
        // contiguous block [3],[4],[5].  The reason is that the cost
        // of starting a new block is a Stop/Start sequence plus another
        // register address byte; the register address byte costs the
        // same as a data byte, so the extra Stop/Start of the separate
        // chunk approach makes the single continguous send cheaper. 
        // But how about this one?:
        //   cccDccDccc...
        // This one is cheaper to send as two separate blocks.  The
        // break costs us a Start/Stop plus a register address byte,
        // but the Start/Stop is only about 25% of the cost of a data
        // byte, so Start/Stop+Register Address is cheaper than sending
        // the two clean data bytes sandwiched between the dirty bytes.
        // So: we want to look for sequences of contiguous dirty bytes
        // and send those as a chunk.  We furthermore will allow up to
        // one clean byte in the midst of the dirty bytes.
        uint8_t buf[17];
        int n = 0;
        for (int i = 0, bit = 1 ; i < 16 ; ++i, bit <<= 1)
            // If this one is dirty, include it in the set of outputs to
            // send to the chip.  Also include this one if it's clean
            // and the outputs on both sides are dirty - see the notes
            // above about optimizing for the case where we have one clean
            // output surrounded by dirty outputs.
            if ((dirty & bit) != 0)
                // it's dirty - add it to the dirty set under construction
                buf[++n] = bri[i];
            else if (n != 0 && n < 15 && (dirty & (bit << 1)) != 0)
                // this one is clean, but the one before and the one after
                // are both dirty, so keep it in the set anyway to take
                // advantage of the auto-increment mode for faster sends
                buf[++n] = bri[i];
                // This one is clean, and it's not surrounded by dirty
                // outputs.  If the set of dirty outputs so far has any
                // members, send them now.
                if (n != 0)
                    // set the starting register address, including the
                    // auto-increment flag, and write the block
                    buf[0] = (TLC59116R::REG_PWM0 + i - n) | TLC59116R::CTL_AIALL;
                    i2c.write(addr << 1, buf, n + 1);
                    // empty the set
                    n = 0;
        // if we finished the loop with dirty outputs to send, send them
        if (n != 0)
            // fill in the starting register address, and write the block
            buf[0] = (TLC59116R::REG_PWM15 + 1 - n) | TLC59116R::CTL_AIALL;
            i2c.write(addr << 1, buf, n + 1);
        // all outputs are now clean
        dirty = 0;
    // Is the unit active?  If we have trouble writing a unit,
    // we can mark it inactive so that we know to stop wasting
    // time writing to it, and so that we can re-initialize it
    // if it comes back on later bus scans.
    bool active;
    // Output states.  This records the latest brightness level
    // for each output as set by the client.  We don't actually
    // send these values to the physical unit until the client 
    // tells us to do an I2C update.
    uint8_t bri[16];
    // Dirty output mask.  Whenever the client changes an output,
    // we record the new brightness in bri[] and set the 
    // corresponding bit here to 1.  We use these bits to determine
    // which outputs to send during each I2C update.
    uint16_t dirty;

// TLC59116 public interface.  This provides control over a collection
// of units connected on a common I2C bus.
class TLC59116
    // Initialize.  The address given is the configurable part
    // of the address, 0x0000 to 0x000F.
    TLC59116(PinName sda, PinName scl, PinName reset)
        : i2c(sda, scl, true), reset(reset)
        // Use the fastest I2C speed possible, since we want to be able
        // to rapidly update many outputs at once.  The TLC59116 can run 
        // I2C at up to 1MHz.
        // assert !RESET until we're ready to go
        // there are no units yet
        memset(units, 0, sizeof(units));
        nextUpdate = 0;
    void init()
        // un-assert reset
        // scan the bus for new units
    // scan the bus
    void scanBus()
        // scan each possible address
        for (int i = 0 ; i < 16 ; ++i)
            // Address 8 and 11 are reserved - skip them
            if (i == 8 || i == 11)
            // Try reading register REG_MODE1
            int addr = I2C_BASE_ADDR | i;
            TLC59116Unit *u = units[i];
            if (readReg8(addr, TLC59116R::REG_MODE1) >= 0)
                // success - if the slot wasn't already populated, allocate
                // a unit entry for it
                if (u == 0)
                    units[i] = u = new TLC59116Unit();
                // if the unit isn't already marked active, initialize it
                if (!u->active)
                    u->init(addr, i2c);
                // failed - if the unit was previously active, mark it
                // as inactive now
                if (u != 0)
                    u->active = false;
    // set an output
    void set(int unit, int output, int val)
        if (unit >= 0 && unit <= 15)
            TLC59116Unit *u = units[unit];
            if (u != 0)
                u->set(output, val);
    // get an output's current value
    int get(int unit, int output)
        if (unit >= 0 && unit <= 15)
            TLC59116Unit *u = units[unit];
            if (u != 0)
                return u->get(output);
        return -1;
    // Send I2C updates to the next unit.  The client must call this 
    // periodically to send pending updates.  We only update one unit on 
    // each call to ensure that the time per cycle is relatively constant
    // (rather than scaling with the number of chips).
    void send()
        // look for a dirty unit
        for (int i = 0, n = nextUpdate ; i < 16 ; ++i, ++n)
            // wrap the unit number
            n &= 0x0F;
            // if this unit is populated and dirty, it's the one to update
            TLC59116Unit *u = units[n];
            if (u != 0 && u->dirty != 0)
                // it's dirty - update it 
                u->send(I2C_BASE_ADDR | n, i2c);
                // We only update one on each call, so we're done.
                // Remember where to pick up again on the next update() 
                // call, and return.
                nextUpdate = n + 1;
    // Enable/disable all outputs
    void enable(bool f)
        // visit each populated unit
        for (int i = 0 ; i < 16 ; ++i)
            // if this unit is populated, enable/disable it
            TLC59116Unit *u = units[i];
            if (u != 0)
                // read the current MODE1 register
                int m = readReg8(I2C_BASE_ADDR | i, TLC59116R::REG_MODE1);
                if (m >= 0)
                    // Turn the oscillator off to disable, on to enable. 
                    // Note that the bit is kind of backwards:  SETTING the 
                    // OSC bit turns the oscillator OFF.
                    if (f)
                        m &= ~TLC59116R::MODE1_OSCOFF; // enable - clear the OSC bit
                        m |= TLC59116R::MODE1_OSCOFF;  // disable - set the OSC bit
                    // update MODE1
                    writeReg8(I2C_BASE_ADDR | i, TLC59116R::REG_MODE1, m);
    // TLC59116 base I2C address.  These chips use an address of
    // the form 110xxxx, where the the low four bits are set by
    // external pins on the chip.  The top three bits are always
    // the same, so we construct the full address by combining 
    // the upper three fixed bits with the four-bit unit number.
    // Note that addresses 1101011 (0x6B) and 1101000 (0x68) are
    // reserved (for SWRSTT and ALLCALL, respectively), and can't
    // be used for configured device addresses.
    static const uint8_t I2C_BASE_ADDR = 0x60;
    // Units.  We populate this with active units we find in
    // bus scans.  Note that units 8 and 11 can't be used because
    // of the reserved ALLCALL and SWRST addresses, but we allocate
    // the slots anyway to keep indexing simple.
    TLC59116Unit *units[16];
    // next unit to update
    int nextUpdate;

    // read 8-bit register; returns the value read on success, -1 on failure
    int readReg8(int addr, uint16_t registerAddr)
        // write the request - register address + auto-inc mode
        uint8_t data_write[1];
        data_write[0] = registerAddr | TLC59116R::CTL_AIALL;
        if (i2c.write(addr << 1, data_write, 1, true))
            return -1;
        // read the result
        uint8_t data_read[1];
        if ( << 1, data_read, 1))
            return -1;
        // return the result
        return data_read[0];
    // write 8-bit register; returns true on success, false on failure
    bool writeReg8(int addr, uint16_t registerAddr, uint8_t data)
        uint8_t data_write[2];
        data_write[0] = registerAddr | TLC59116R::CTL_AIALL;
        data_write[1] = data;
        return !i2c.write(addr << 1, data_write, 2);
    // I2C bus interface
    I2C_Type i2c;
    // reset pin (active low)
    DigitalOut reset;