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AN S-7600A/PIC16F877 JOURNEY

Part 1: Laying Out the Tools
by Fred Eady

Start ı Tooling Up ı Hardware Development Tool ı Software Development Tools ı Selecting a Terminal Emulator ı The Boot Loader ı Add Virtual Paper ı Sources and PDF

TOOLING UP

If you followed my Ethernet series, you know that I provided a glimpse into the bits and bytes of Ethernet using Network Associateıs Sniffer. The S-7600A/PIC16F877 Internet Engine depends on PPP (point-to-point protocol) over an asynchronous link to use the services of the Internet. Furthermore, a standard async link is used to transfer operating code from a host computer to the S-7600A/PIC16F877 Internet Engineıs flash memory-based microcontroller.

I want to show you the low-level details of this project, too. My first go at that was to bring out my hardware data scopes with the hope that I could transform the data formats to something you could easily understand and view online. That didnıt happen. The printouts were cryptic and I spent a lot of time trying to clean them up for publication.

My second try at getting some viewable data captures had me turning to a software product I had on the shelf of the Florida room. I wonıt mention a name because that wouldn't be fair. Although the product did perform the tasks it was designed to do well, the features I needed for this article were not there.

The third try was indeed the charm. I contacted Stephen Liberman at Frontline Test Equipment to inquire about a product he offered called Serialtest Async. After reading some reviews on the product and downloading the demo, I had just what I needed to convey the low levels of protocols that were used to bring the S-7600A/PIC16F877 Internet Engine to life.

Serialtest Async is part of a family of products that comprises the Frontline Test System (FTS). The basic idea is to provide a tool set that allows you to use a laptop, embedded, or desktop personal computer to perform data analysis. Serialtest Async is a rich product, but because of the intuitive interface, I was able to use it right out of the box.

Serialtest Async comes with a cable set that allows you to either monitor a circuit or inject signals into a circuit. Hereıs how that works. A y-cable called a routing cable (see Photo 2), consisting of a DB-25 female at one end and two DE-9s labeled DCE and DTE at the opposite end, connects to either a monitor or source head. The heads are identical with the exception of the source head being labeled with DTE and DCE markings (see Photo 3).

If your computing deviceıs serial ports have DB-25 connectors, a set of DB-25-to-DE-9 adapters is also included with the Serialtest Async package. The instructions for how to connect the cables are included in the online help and are clear. I only want to monitor the communications channel between the S-7600A/PIC16F877 Internet Engine and a terminal program running on a PC.

I also have two open serial ports I can use. So, I chose the two-port "monitor a circuit" link in the help text. I was instructed to plug the DE-9ıs DTE and DCE ends of the routing cable into serial ports 1 and 2. The DTE end was plugged into COM1 and the DCE end was inserted into the COM2 port. I then connected the monitor head to the DB-25 side of the routing cable. All that was left to do was plug in my S-7600A/PIC16F877 Internet Engine, which is configured as a DCE to one side of the monitor head and plug in the serial port cable from the PC running a terminal emulator to the other open monitor head port.

Basically, I used the monitor head as a "T" to tap and route data from the PC terminal emulator and the S-7600A/PIC16F877 Internet Engine to the computer that is running Serialtest Async. If you have only a single serial port, the monitor and inject data options are identical, with the exception that you canıt simultaneously monitor DCE and DTE data with a single COM port. By the way, Serialtest Async runs under all of the Windows platforms that you can currently purchase.

If you have no COM ports, you can actually plug into another product called Spy, also from Frontline. Like Serialtest Async, Spy is an FTS component. Spy allows you to monitor and analyze data generated by a COM port or internal modem. You can actually run FTS and a separate communications application on the same computer. Internal modems look like COM ports ("tastes like chicken"), and Spy is able to see this exchange of data. This is made possible by a custom FTS serial device driver.

To give control to the FTS serial driver, you must start the FTS application before starting the coexisting communications application. FTS, the COM port being monitored and the secondary application must be able to use the FTS serial driver. I also have a copy of Spy, and Iıll take a closer look at it later.

FTS is based on a control window like the one you see in Photo 4. The buttons are not unlike any other Windows-based buttons and each icon is representative of a window or data capture function. I wonıt go into detail about what each button does here as you can use the mouse pointer to get a description of each button by simply placing the cursor over the button. Much can be learned about the configuration of Serialtest Async by glancing at the fields in the control window. The link speeds and COM port definitions are just a couple of bits of information you can find here. I could write a couple of articles on just the operation of Serialtest Async. Instead, Iıll show you real-time shots of data exchanges between the PC terminal program and the S-7600A/PIC16F877 Internet Engine.

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