SXmicro.com

Check out Michael Kohn’s web site. He used an SX to create a VGA signal. This a good example of a simple project that harnesses the raw speed of the SX.

When you were reviewing page 6 of the SX data sheet you might have noticed the pins labeled Vdd and Vss. These pins are the power pins of the chip. The SX can have a voltage from 2.7V to 5.5V DC on its power pins. The minimum voltage allowed is a function of the frequency that the device is operating at. For now, we will mostly use 5V DC in our experiments.

Now, which pin is positive and which pin is negative or ground? At the bottom of the table on page 6 we learn that Vdd is positive and Vss is ground. I don’t know any good memory tricks to help you remember this one. If you have a memory trick, let us know in the comment section.

If you are interested in the history and further understand of Vdd and Vss you should check out this entry in Wikipedia.

Did you download and review the first 8 pages of the SX20/SX28 data sheet like we recommended in our previous post? If not, go ahead and do it now. In this post we will go over a few of the highlights of the first few pages.

Page 1: This page contains an exciting text description of the SX as well as a block diagram of the internal SX operation. Look at the diagram for a couple minutes and soak in the terms you see there. What else do you see? I see a lot of “8″s everywhere. All those “8″s are indicating a register size (when the 8 is in a box like “8-bit timer”) or a bus width like the “/8″ seen on the lines in between boxes. What is that? A /12 on the instruction bus? Hmmm….we shall investigate that later.

In the upper left of the diagram we can see that there is an internal 4 MHz. oscillator and two connection points for an external oscillator.

Page 2: Table of contents, not much else to say.

Page 3 & 4: Here we can find the key features of the SX. If you want to be a real geek, you should memorize these and repeat them randomly when talking to family and friends. Ok, just kidding. For now read through them and, again, soak in the terms. If you don’t know a term then flip to the next page and see if reading through page 4 helps. Page 4 is a word description of the architecture. This page may confuse you more but in time it will become more clear. Also be sure to try Wikipedia for article entries on terms or post your questions in the comments.

Page 5: There is only a table on this page and the part numbering scheme for the SX. The SX has only a couple variants, otherwise each IC is nearly the same. Look at the table and you will see that the operating voltage, memory and temperature ranges are nearly identical. The only real difference is in the IC package and the quantity of I/O pins. Thank goodness we don’t have to memorize odd numbers and labeling to indicate which MCU we are using. An SX28 is an SX28 with only a slight variation between the IC packages. See the next page….

Page 6: You will refer to this page often. At the top of the page is a diagram of each SX IC package and the labeling for what each pin function is. Below the diagram is a table to explain further the pin function. This is important information. One thing to highlight on this page is that the SX28 SSOP package and DIP package are slightly different. Look at the pins on the left side of each package and you will find they are in a slightly different order. Take note of this if you layout a circuit board!

Page 7 & 8: These two pages show how to connect to an SX microcontroller. The SX-Key is used to program the SX. Besides the SX-Key the MCU will need a voltage and a pull-up resistor or two. If you look at the schematics for the SX Tech Demo board, you will find they are similar to this. In fact, if you look at any device using the SX they all pretty much have this core schematic in them.

One very, very important thing to note is how the SX is programmed. Data from the SX-Key is transferred into the SX via the OSC1 and OSC2 pins. Remember earlier that we said the OSC1/2 pins were for an external oscillator? The point here is that the oscillator must be out of the circuit when it is attached to an SX-Key. Later on you will see how we work with this.

Oh, another note, the SX-Key USB does NOT provide power to the SX. You must ensure that the SX circuit is powered from a separate DC source in order to program and use the SX and the SX-Key USB together. An example of this is the scrolling text medal. The batteries must be installed and the device turned on for the SX to be programmed by an SX-Key.