Nuts and Volts - September 2015

variable. In the first syntax variation above, the mask parameter of the setintflags command can be used to specify which flag bit(s) we want to trigger the interrupt; any flag bit masked by a “0” will be ignored. The setintflags command allows for various combinations, but we’re only interested in the hserinflag (bit 5 of flags), so we’ll specify mask as %00100000, and ignore all the other flags.

The flags parameter can be used to specify which condition (high or low) of the flag(s) we want to trigger an interrupt. Again, we’re only interested in the hserinflag which is automatically set to “1” (high) when background serial data is received. So, we will also specify flags as %00100000. Actually, because we’re ignoring all the other flags, it doesn’t matter what value (0 or 1) we place in any of the other bit positions, but it could be confusing to change any of the other zeros to ones.

By now, I’m sure you’re glad to hear that we’ve finally covered all the theoretical details that we need for our first experiment! This would be a good time to take a break and maybe stretch a little. When you’re ready, we’ll move on to our first experiment.

Experiment 1: Hserin with an Interrupt and Direct Addressing

This experiment is very similar to our two 20X2 experiments from last time. The main difference is that we will be using the hserinflag interrupt this time.

Figure 1 presents the schematic for both experiments this month, and Figure 2 is a photo of my breadboard setup. As we did previously, we’ll again be using the Cool Term program (or whichever terminal program you prefer) in line mode, so that we can type a complete line of text and then press the enter (or return) key on the Mac or PC to transmit the entire line of serial data to the 20X2.

I also again used 115,200 for the baud rate, but if you had any problems with that previously you may want to drop back to 57,600 baud. (We’ll discuss baud rate changes shortly.) When you’re ready to configure your terminal program for the experiment, be sure to specify the following settings: • In the “Serial Port Options,” select 115,200 baud and whichever serial port your PL2303HX cable is connected to. (Mine always shows up as “usbserial;” the same may be true for your cable.)

• In the “Terminal Options,” select “Line Mode” and enable the “CR+LF” option for the “Enter Key Emulation.” The software for Experiment 1 ( Hser20X2IntDirect.bas) is available at the article link. Now would be a good time to get it, along with the other program we’ll be using this month. Before you run the program on your 20X2 breadboard setup, let’s take a look at the details of the interrupt subroutine. (You may want to print a hard copy of the program as a reference for our discussion.)

As usual, the following numbered

12 September 2015

Post comments on this article and find any associated files and/or downloads at www.nutsvolts.com/index.php?/magazine/article/september2015_PICAXEPrimer.