Note: I have written a post containing updated compatibility information you may want to read here. The remainder of this post below is still very important, but I’d like to make sure everyone has the most up-to-date information about compatibility between the different DLLs and parallel port cards out there. If you’re looking for my patched io.dll for Willem programmer compatibility, see below.

Last year I bought a Willem EPROM programmer board from Sivava. It’s basically a cool little board with various sockets for plugging in EPROM/EEPROM/Flash/etc chips for reading/erasing/writing. Apparently it can even program some AVR microcontrollers. I have the PCB50 version of the board.

Here’s the deal. It has a USB port, but it’s only for supplying power. All communication goes through the parallel port. As everybody should know at this point, the parallel port is on the way out. No, scratch that. The parallel port is long gone. I had to use a really old HP Pavilion with a Celeron running Windows 98 to do anything with it. The programmer worked great, and I was able to fix a computer’s BIOS chip that I had messed up while trying to hack its BIOS.

Let’s fast forward to over a year later (a.k.a. now). I have a homebuilt PC with an Intel DX58SO motherboard and a Core i7 CPU, running Windows 7 Ultimate edition, 64-bit. The DX58SO literally has no legacy peripherals, other than a single PCI slot. It has no PS/2 ports, no parallel port, no serial ports, and no standard IDE ports. It does have a variety of types of PCI Express slots, though.

I recently bought a sweet PCI Express 1x card with four serial ports and a parallel port from Newegg. (Note: Newegg’s product specs lie about this card — the parallel port does not support EPP or ECP mode, according to a sticker on the box, even though Newegg says it does). I remembered that I had my programmer and decided I totally needed to get it working in Windows 7.

Easier said than done.

It’s difficult enough to get low-level legacy stuff working in Windows 7, but when you’re using the 64-bit edition, a lot of older stuff breaks even more. Also let’s remember that add-on parallel ports do not get mapped to the standard I/O addresses for parallel ports (0x378 and 0x278), but instead some other random address (mine is at 0x3000). I tried running the software that came with the board, but it just gives me errors and actually won’t let me exit without forcing it to quit from the task manager.

Let’s go on a Google adventure. Google lesson #1: sometimes when you’re looking for info about Windows 7 64-bit, you can find very useful stuff when you search for Vista 64-bit (or XP 64-bit) instead. My first search was willem vista 64-bit.

The second result was a digg posting titled Willem Eprom for Vista and 64bit XP (digg post is no longer available; link removed). The linked page is a forum posting at a forum called The post is by the admin of the site, and he mentions to install software called TVicPort and then a modified io.dll file. The first comment on the digg posting was by a user named rabitguy, who said he had a Willem board working on Windows 7 64-bit with tvicport and iodllwrapper.

So I kept seeing this io.dll and iodllwrapper stuff. What exactly is it? Let’s Google for “io.dll”.

The first result is to a homepage for io.dll. Basically, it explains that it’s a library allowing direct port access from several different Windows versions. Awesome! Except it doesn’t mention Windows Vista or Windows 7, or anything 64-bit at all. Crap. Well, I looked in the installation directory for the Willem software that came with my Sivava programmer board, and sure enough, in C:\Program Files (x86)\EPROM50, there’s an evil file named io.dll. So that’s why it doesn’t work.

So anyway, I searched for iodllwrapper, deciding to follow the advice of rabitguy. The first result is to a forum posting on an Amiga message board. I did a search on that page for “Willem” and found a posting by Toni Wilen who wrote a 64-bit-compatible io.dll wrapper which depends on TVicPort and uploaded it as an attachment to the forum, called He even included the source code. Aha! So I think I get it. He wrote a DLL that provides all the functions that io.dll would provide, except rather than implementing the raw functionality himself, he forwards the relevant function calls to TVicPort, which handles all the low level stuff (in a manner that works on 64-bit operating systems!). Actually it’s a pretty genius idea. So I downloaded his DLL and tried it out, replacing the stock io.dll file that came with the Willem software with his new wrapper.

I crossed my fingers and opened the programmer software. Awesome! I no longer got a bunch of weird errors when the program opened! I’m pretty sure Toni’s DLL would have worked great, but there’s a problem in my case. I don’t have a built-in parallel port, so my parallel port is at a non-standard I/O address (0x3000). The Willem software only lets you choose from a list of three standard I/O addresses where built-in parallel ports would appear.

Ugh! So I was stuck again. At this point I was about to throw in the towel. But first, I thought about it and came to the conclusion that I can’t be the only one with this problem. So I searched for io.dll willem address.

The first result this time was Ben Ryves’ Remapped IO.DLL. So someone else had the exact same problem! Ben also wrote an IO.DLL wrapper (and he included his source code, too!). His solution is to add an additional file called io.ini into the same directory as io.dll. You put the I/O address of your parallel port into that file (so my io.ini file would contain one line — 0x3000), and set the Willem software to use LPT1. The wrapper DLL looks for any I/O reads/writes in the LPT1 range and remaps them to actually occur at the address specified in the io.ini file. This is exactly what I needed!

It uses another DLL called inpout32.dll to do the dirty work. Actually, Ben’s site very nicely describes everything his DLL does, so I won’t go into any more detail about it.

Well, it turns out that his DLL didn’t work for me, either. It seems that it’s just not compatible with 64-bit Windows 7, at least in my experience. I just could not get it to work. The Willem software would not detect the connected board. I looked at the homepage for inpout32, and apparently there is a 64-bit version, so maybe if I had fiddled long enough I could have gotten inpoutx64 to work, but at this point I actually had an idea of my own, after looking at the source code that Ben included for his DLL.

I knew from everything I had read that Toni’s 64-bit-compatible io.dll wrapper using TVicPort did work. All it was missing was the remapping. So I took Ben’s code and modified it to use TVicPort rather than inpout32.dll. (Alternatively I could have added the remapping to Toni’s code.) I only changed a few lines. I just changed the calls to inpout32.dll for reading/writing to use the corresponding TVicPort functions instead, and also added initialization and deinitialization code for TVicPort.

So I compiled it with Visual C++ Express Edition 2008…ran the “Test Hardware” function on the Willem software…and success! It found the hardware! I was stoked, so I grabbed a BIOS chip from an old motherboard I’m not using anymore (Asus A7V133). It’s a SyncMOS F29C51002T. I chose that model in the software, set up the DIP switches correctly, and stuck the chip in the cool ZIF socket on the programmer board. I then read the BIOS from the chip. I looked at the read buffer and it looked good! I saw stuff about an Award BIOS, so it sure looked like it was working. I happened to have a good copy of the same BIOS file from when I had messed with that same chip on the older computer, so naturally I did a diff against them to make sure that the file was read correctly.

It didn’t read correctly. It differed by just a few bytes. It was mostly OK, but mostly is not good enough when you’re reading to/writing from chips that contain computer code and/or data. At this point I decided to sleep on it and think about it the next day. That approach really works well in all aspects of life in my experience. When I had trouble learning to play a piano piece I would sleep on it and the next day it was like my brain had somehow prepared itself ahead of time, and I would play the part I had been struggling with perfectly.

The next day I noticed that the TVicPort driver actually has an option for two I/O port access “modes.” The default mode is hard mode, which is slower, but provides more reliable access to an I/O port if it’s already been opened by a different driver. Soft mode is faster, but has trouble if a port is already open by another driver. On a whim I decided to try out soft mode. I read the chip again, and this time it worked perfectly. I then erased it, wrote the file back, and compared it. Perfect. I did this several times just to make sure I wasn’t getting lucky, and it worked every time.

So either I got really unlucky on my first try with hard mode, or using soft mode fixed it. I don’t know which one is the case, but regardless, I now have my programmer working in Windows 7 64-bit. And this is the end of our Google adventure.

Google can do a lot of great things if you’re willing to sit down and search. And search. And search. I didn’t actually find all this stuff that easily. I tried many different searches, wording things slightly differently. I ended up only showing you guys the search queries I tried that gave me interesting results.

So…thank you to everyone I mentioned in my post. I’ve never met you or even corresponded with you, but you all helped me get this working. Thank you rabitguy, admin at onecamonly, Toni, and Ben. With all of your info I got it working.

So naturally, here’s my io.dll wrapper, based on Ben’s wrapper, along with the source code for it.
Remember, I’m not responsible for any damage done by this software–it’s been tested lightly and seems to work for me, but your mileage may vary!
Download 64-bit remapped IO.DLL wrapper and source code (new version 1.1 which fixes a bug–thanks Paco!)
You will also need to download TVicPort from here.

Install TVicPort, then restart your computer (mine didn’t work until I restarted, and it does ask you to restart). Replace the io.dll file in the Willem software directory (C:\Program Files (x86)\EPROM50 on my computer) with this patched version. Open up the io.ini file, replace the address there with your parallel port’s I/O address (make sure you keep the “0x” before the address or it won’t work), and put it in the same directory you just copied the DLL file to. Set the Willem software to use LPT1 (0x378). If everything is working correctly, you should be able to go to the Help menu and choose Test hardware, and it will say “Hardware present” in the status bar at the bottom.

If you need to compile the modified io.dll for yourself or make modifications, grab TVicPort.h and TVicPort.lib from the TVicPort installation (C:\TVicPortPersonal\Examples\MSVC) and put them in the project directory. After doing that it should compile.

Hope this helps anyone out there, and thanks again to everyone whose information and source code helped me out!

A quick note: To find your parallel port’s I/O address, go into the Device Manager and open up your parallel port. It’s in the Resources tab:

The I/O range that is 8 bytes long (in my case, 3000-3007) is the important one. So prefix the start address with 0x (so in my case, I ended up with 0x3000) and that’s the value you should put in the io.ini file.

Version History:

  • 1.1 – Fixed a bug where I was calling functions from DllMain that I should not have been calling, causing the DLL to not work for at least one person – August 15, 2011. [Download]
  • 1.0 – Initial release – October 9, 2010. [Download]

I couldn’t resist jumping into my “microcontroller programming for high level programmers” series as soon as possible, so I’d like to go into a bit more detail about where I left off in my last post–memory-mapped peripherals.

Like I said in my last post, I missed out on memory-mapped peripherals during my CS education (which is not too surprising). My mental model for how memory addresses work was missing a chunk of knowledge. I thought that every memory address was a storage location–either RAM (readable and writable) or ROM (only readable). It turns out that memory addresses in computers can also be used for other stuff, like telling an external chip or a built-in peripheral to do something.

A memory-mapped peripheral works exactly how I just described. The peripheral reserves a portion of the address space on the computer. You write to (or read from) somewhere inside that address range, and the peripheral does something in response. Let me give you a simple example:

Let’s pretend that a microcontroller has an “LED” peripheral. By LED I mean a light-emitting diode–a little green or red or whatever other color light. Get used to the acronym “LED” because it’s very common. An example of an LED is the power light on your computer. Anyway, back to the pretend world. Imagine that the physical microcontroller chip has eight pins you can hook up to LEDs to light up, and your program can control them. The “LED” peripheral is mapped to memory location 0x1234, and it’s one byte long. Each of the eight bits in the byte controls one of the LEDs. If a bit is one, its corresponding LED will be turned on, and if the bit is zero, its corresponding LED will turn off.

In a C program, you would then turn the LEDs on and off by changing the value at address 0x1234. I’m going to assume you understand pointers. I’m creating a pointer so that I can manipulate the LED peripheral. Remember that uint8_t is usually typedef’d as unsigned char–an 8-bit integer that has no sign bit, so you can mess with all eight bits without worrying about side effects. Here’s some sample code:

#include <stdint.h>

/* Get a pointer to the LED peripheral */
/* Note that you cannot do this in Linux in a user program */
/* because each user program has its own virtual address space */
/* and other sections of memory are protected from direct access */

volatile uint8_t *LED = (volatile uint8_t *)0x1234;

/* Turn all LEDs off */
*LED = 0;

/* Wait for 1 second -- just pretend this is already implemented */

/* Turn every other LED on -- 0x55 == 01010101 in binary */
*LED = 0x55;


/* Turn on the LED associated with bit 7 -- 0x80 == 10000000 binary */
*LED |= 0x80;


/* Turn off the LED associated with bit 0 -- 0x01 == 00000001 binary */
*LED &= ~0x01;

Ok–I hope that wasn’t too much to start out with, but I’ll try to explain in detail what I did.

First, I created a pointer that points to the LED peripheral’s address (0x1234). I said earlier that the peripheral is one byte long. That’s why I picked a uint8_t as the type — because a uint8_t is 8 bits, or 1 byte, in size.

You may have noticed that I defined the pointer as volatile. Why did I do that? I’ll tell you as soon as I finish explaining the rest of the code. It will be easier to describe what it does as soon as you understand exactly what the code does.

After that, I write a zero to the LED peripheral. Remember that since the variable “LED” is a pointer, I have to use the * operator to tell it to write to the address to which LED is pointing. Since every bit of a zero byte is zero, this turns off all the LEDs (if any were on already). Next, I call an imaginary function to wait for 1000 milliseconds, or in other words, one second.

Then, I write 0x55 to the LED peripheral, turning on the LEDs associated with bits 0, 2, 4, and 6. Of course, I wait a second here too.

For the last few operations, I turn on the LED associated with bit 7 (without affecting the other LEDs), wait another second, and then turn off the LED associated with bit 0 (again without affecting the other LEDs). If you haven’t seen the bitwise operations |, &, and ~ used much in C, you should definitely learn them before venturing onward. They will be used endlessly to manipulate individual bits in memory-mapped peripherals. Sometimes you want to turn on a single bit at an address while leaving all the rest of the bits unchanged. The | operator is perfect for this. Likewise, the & operator (combined with ~ for a bitwise NOT) works great to turn off a single bit without affecting the other bits. Study those two lines in my example code carefully until you understand exactly what they are doing.

If you were to run a program like this on a real microcontroller that had a real “LED” peripheral, you would physically see the LEDs changing each time the corresponding code wrote to the LED memory-mapped peripheral.

Back to the volatile keyword for a minute. Declaring a pointer as volatile forces the C compiler to always access the memory address a pointer points to, no matter what, with no optimizations allowed. You’ll notice that I write several different values to the LED peripheral in this program. A good compiler might notice that I first write 0 to it, then write 0x55, then turn on bit 7 (effectively writing 0xD5) and then turn off bit 0 (effectively writing 0xD4). It might think “hey, why should I do all these intermediate operations? I know that it will effectively end up with the value 0xD4, so why not just write that in directly?” For normal variables in a program, this could very well be a great idea to make your program run faster, because it would save unnecessary arithmetic operations from needing to be performed. For memory-mapped peripherals, it’s not such a great idea, because those intermediate values being written to the peripheral actually have a meaning. The volatile keyword simply makes sure the compiler does not make any optimization decisions like that. Whenever you’re accessing a memory-mapped peripheral, a pointer to it should be defined as volatile.

I will finish off this first real post of the series with a reality check. In my experience, there’s not really such thing as an “LED” peripheral. Instead, what you end up using is a “GPIO” peripheral. GPIO stands for General Purpose Input/Output. A microcontroller might have several “ports” — port A, B, C and D, for example, each eight bits. The physical chip would have pins corresponding to each port. Port A pin 0, port A pin 1, and so on. There would also be corresponding memory-mapped peripherals for each port. So if you had LEDs hooked up to port A pins 0 through 7, you could then do exactly what I showed in my “LED” example, except you would write to the GPIO port A peripheral, which would be memory mapped similar to how I described before.

It’s a little more complicated than that because I only really described the “output” capabilities of GPIO ports. You can also configure GPIO pins as inputs, so they read data from an external source and your program can see whether they are “high” or “low”. I hope that makes sense, and I’ll go into more detail about GPIO in the future. The memory space of a GPIO peripheral is more than just a byte wide. There are other sections of its memory space for configuring things like whether a pin is input or output, and also pull-up/pull-down resistors for inputs. In general, you will see these various sections of the memory-mapped address space referred to as the peripheral’s “registers.”

Anyway, that’s all for this first post. If you happen upon this post and have any questions, feel free to ask in the comments and I will try my best to answer them.

When I went to college, I majored in computer science. I took classes about algorithms, data structures, software engineering, design patterns, systems analysis and design (now that is a BORING topic!), web development, databases, operating systems, and even assembly language and computer architecture. To be honest, I actually thought those last two classes I listed were some of the more interesting topics my education covered (and they were both electives, not really part of the core CS curriculum). Maybe that’s a sign I should have done more in the computer engineering side of things. I don’t know for sure.

I’m not saying I didn’t enjoy my CS education, because I did! It was awesome, and I always looked forward to taking my CS classes. I was a math minor as well, and as you can probably guess, I enjoyed taking math classes. I actually took more math classes than I needed (such as operations research) just because they were fun. I guess my point is that I’m not dissing on my CS education; I’m only trying to point out that I had multiple interests in college.

After graduating college, I ended up working at a place that does a lot of work with microcontrollers. I’ve also written some “ordinary” desktop or web-app software, but I’ve found myself really enjoying the work with microcontrollers. As a person with a bachelor’s degree in computer science, I didn’t have any trouble picking up on the concepts. After all, computer science is not a “here’s how to program a generic desktop application in Visual Studio” type of education. You can apply what you learn to many different fields. But in order to fully understand the concepts, you have to do examples, at least in my opinion. And the examples I did in college were C/C++ console applications running on Linux, Java console and GUI applications, shell scripts, and websites in various flavors such as Java servlets, JSP, ASP.NET, PHP, and Ruby on Rails. All of this stuff is pretty high-level–even C apps running on Linux are high-level compared to bare metal code. So in doing this, I understood the general computer science ideas that the curriculum was actually teaching, but I didn’t really have any kind of concrete experience with directly programming to a microcontroller. Even in the assembly class, we ran programs on floppy disks inside of DOS, so that wasn’t bare metal either.

So as you might expect, when I first started at the place where I work, I knew literally nothing about how to use microcontrollers. I had no idea how microcontrollers actually did anything. I remembered from my assembly language class that x86 machines use a software interrupt instruction to talk to a PC’s BIOS, but that was about it. I heard my coworkers throw around terms like “SPI”, “I2C”, “UART”, “GPIO”, “PWM”, “DMA”, “CAN”, “Timers”, “Watchdog”, and all that kind of stuff, but had no idea what they meant.

Luckily, I have become familiar with this stuff (thanks to reading datasheets and my awesome coworkers, of course!), and once you get down to it, it’s really not complicated. It turns out I didn’t understand what goes on inside computers at one specific level. My computer architecture class was at too low of a level (transistors, gates, adders, ALU, etc.), and my assembly language class was at too high of a level (this is what registers are, this is what instructions are, here’s an example of how you multiply two numbers in the x86 instruction set, now go make your own DOS program that uses DOS and/or BIOS interrupt routines to do something cool), if that makes any sense at all.

I think it’s important to understand both of those levels, but there’s a level in between as well. I think I’ll call it “memory-mapped peripherals.” It turns out that microcontrollers have a bunch of special extra devices built in to assist you. They might do stuff like communicate with another chip that’s connected to it or display a message on an LCD display. Ok, so memory-mapped I/O is not really a “level”, but it points out a concept that somehow slipped through the cracks of my education.

So anyway, I’ve decided I’m going to write a series of posts about how to do microcontroller programming from the perspective of someone who has experience with “normal” application programming. I’ll try to teach all the stuff that datasheets just assume you know. I’m sure there are people out there with this same kind of issue. I know I was one of them! If you’re interested in this, stay tuned, and I will start doing more posts! Below is a list of posts in this series I have already written, and I’ll keep it up to date as I add more.

Posts in the series: