Bailey O.H.Embedded systems.Desktop integration.2005

If you used terminals as directed in step 14, your board will look similar to the following.

Figure 7-12

Next, we will solder the wires to the DB9 so we can attach it to an RS-232 cable. This is very simple.

1.First, cut eight pieces of wire about 4 inches long and strip 3/8 inch of insulation from each end.

2.Now solder each wire to the DB9 by inserting the wire into the connector as far as it will go. Apply a small amount of solder around the joint where the wire and connector are joined. Do not use too much solder or apply the soldering iron for too long since the area around the connector is plastic. Solder all eight wires.

3.Apply a small amount of solder to the other end of each wire to prevent it from fraying. Just apply a small amount to change the color of the copper wire to silver.

4.Next, using either a wire nut or a small piece of electrical tape, connect the wires together that are attached to pins 1, 4, and 6. This will tie the carrier detect (DCD), data- terminal-ready (DTR), and data-set-ready together (DSR).

Figure 7-13

Remember to use a female DB9 connector!

Testing the RS-232 Interface

We have finally reached the point where we are ready to connect and test the RS-232 board. To do the testing I’m using the BASIC Stamp 2p Development Board, the RS-232 board, the DB9 connector we made, and a PC running Windows, FreeBSD, or Linux. At this point we will install and run MicroComm, a simple terminal program I wrote for this project RS-232 board.

Setting Up the BASIC Stamp Development Board

We will begin by setting up the jumpers on the BASIC Stamp Development Board. To allow plenty of space for your fingers, jumper BASIC Stamp pins 15, 14, 13, and 12 from the connector to the prototype area of the board as shown in Figure 7-14.

Figure 7-14

In Figure 7-14 the +5 and Gnd at the very top are connected to the power and ground connections on the RS-232 board. The DB9 Gnd connection is attached to pin 5 on the DB9 to provide a common ground. This connection is required to assure data integrity. On the far left side at the top are BASIC Stamp pins 15, 14, 13, and 12. They are connected to the MAX232CPE pins as follows:

Stamp pin 15 Max232 pin 9

Stamp pin 14 Max232 pin 12

Stamp pin 13 Max232 pin 10

Stamp pin 12 Max232 pin 11

With these four connections we have hooked up our TTL data and handshake lines. Next, we move on to the RS-232 board and hook up the RS-232 signal lines.

In Figure 7-15 we connect the RS-232 level signals to the DB9 as follows:

Max232 pin 7 DB9 pin 8

Max232 pin 8 DB9 pin 7

Max232 pin 13 DB9 pin 3

Max232 pin 14 DB9 pin 2

a channel 1 probe to the transmit data line and attach the ground to pin 5 on the DB9. Set your voltage levels to at least 2 volts (preferably 5) and your timing to 5 ms. If data is being sent, the data bits should be able to be disguised at this speed. If no state transitions are seen, then go back and check your circuit to be sure everything is connected properly, power is properly connected, and a good ground connection has been made.

Finishing Touches

To finish our RS-232 hardware setup, connect a serial cable between a host PC and the BASIC Stamp board. Apply power to the board and start the BASIC Stamp Editor program. To test our RS-232 board, enter the following program into the editor:

Listing 7-1

//

//{$PBASIC 2.5}

//Test Program for RS-232 output using MAX232 with RTS/CTS Handshaking

//for Embedded Systems Desktop Integration

//Copyright 2004 - Oliver H. Bailey

//

// Pins are assigned in the following order:

//This program uses the FPin variable on SerIn and SerOut commands. Example follows below

//Serout 12\15, 110, "Mary had a little lamb" CR, LF

InData VAR Byte

OutData VAR Byte

Main:

Figure 7-16

If everything is wired correctly, anything you type in the terminal window will be echoed in the terminal. The uComm program is set to full duplex. This, combined with the fact that both SERIN and SEROUT in the above Stamp program use hardware handshake lines, causes the characters to be echoed when typed. When uComm starts, the Use RTS option is unchecked. If you move the cursor to the terminal window and begin typing, you will see the TX Data LED turn red but nothing typed will be echoed back. The reason for this is because the RTS line has not been used to handshake with the Stamp. Type a few characters and then check the Use RTS box. Now you should see the characters you type displayed as you type them. This means the CTS/RTS handshake is working; otherwise, nothing would be displayed. If you checked Use RTS and still don’t see any characters that were typed, try checking your wire connections to be certain everything is connected properly.

both a simple, light-duty 1-Wire network and a medium-duty 1-Wire network. Before continuing I should note that operating 1-Wire devices over long distances should be done using Cat 5 Ethernet cable, which is the same cable used in computer LANs. Cat 5 cable offers the best choice of line resistance over long distances.

There are many types of 1-Wire devices but for our purpose we are concerned with just four types, discussed in the following sections. In order to make effective use of a single wire for data these devices are broken down into device families, each with a unique family code or family ID. In addition to the family codes, each 1-Wire device has a unique address (or serial number) that no other 1-Wire device has. This address can identify a location, a specific device, a board, or even be used for a product serial number. Depending on the device type, each device also has a set of commands to read, write, and perform other tasks associated with the functions of that particular device family.

When using a 1-Wire temperature chip, there are commands for converting and returning the current temperature, setting high and low temperature alarm level, and reading temporary memory. On the 1-Wire switches and variable potentiometers there are commands for opening and closing switches, and setting and reading the potentiometers. Devices like the DS2404 also support multiple interface protocols at once, which allow them to be used as a data drop station for a local processor. This means the clock function could be addressed using the 1-Wire interface while the onboard static RAM could be addressed using the 3-Wire interface for higher speed memory access by a local processor. This is how dual-port RAM works.

The DS1820 and DS1822 Temperature Chips

The DS1820 temperature chip is a high-resolution temperature chip. It utilizes the 1-Wire network and is used where accurate and high-resolution temperature tracking is required. The DS1822 is a very cost-effective digital thermometer and temperature conversion chip. The DS1822 is less expensive but offers