Views of RS-232 Option Installed or Missing

Open the CP-1 so that the rear of the unit is facing you. Look in the left corner next to the power supply connector. (Top image) The RS-232 option has been installed from the factory. The DB-25 connector, IC U12 and U13, are present along with several other components. (Bottom image) Noticeably the DB-25 is missing out the back of the CP-1 as are IC U12 and U13 nearby. Components either side of the two empty sockets are missing as well. Just because there is a DB-25 connector on the back of the CP-1 does not mean the RS-232 option was installed at the factory. CP-1's usually came without the DB-25 connector. However, some came with the connector, but not the necessary components! The only way to tell for sure is to pop the lid off and check. There are two IC's responsible for handling the RS-232 interface in the CP-1. The part numbers are: 75150 and 75152 (U12 and U13). Look for these two IC's near the female DB-25 connector...or where it should be. If the two IC sockets are empty The RS-232 interface option is not installed. Not only are the two IC's missing, but components: Q12, R99, R100, R121 through R124, D29, and possibly the DB-25 connector are missing as well. There are several options available to upgrade the CP-1. If the two IC's and other RS-232 parts are installed Then you have a prize! However your CP-1 will not be simply "Plug-N-Play" (nothing ever is) with an ordinary serial cable. Some simple re-wiring will be needed. See details.

If the two sockets are empty (No RS-232)
There are three options:

Option #1 - Make RS-232 using a Maxim MAX232, MAX203, or MAX202 IC (Recommended)
This truly is the easiest way to go for all your TTL to RS-232 designs. Maxim chips are available from many suppliers, or Maxim direct. Better yet, you can send off for a free sample! See the parts resource page for details. The Maxim chips I would recommend are: MAX232, MAX202E, or MAX203E (no external components needed for MAX203E.) Below is a schematic of how I built and wired in my RS-232 interface. If you wire your interface as I did in the schematic below, you can use a standard, unmodified, serial cable! You may also want to have a look at my TTL to RS-232 interface page for more details and other RS-232 interfaces in general. You may have difficulty finding the right DB-25 board mounted connector to extend out the back of the CP-1. I have a simple solution to the problem.

Option #2 - Find and install original parts
Locating a source for the 75150 and 75152 is difficult as they are discontinued IC's. If you do, the minimum order, and shipping/handling will easily put this project over budget. If you go this route, you will need to make your own serial cable. You may have a difficulty finding the right female DB-25 board mounted connector to extend out the back of the CP-1. I have a simple solution to the problem.

Option #3 - Original AEA CP-1 service bulletin
AEA CP-1 service bulletin (80K zipped) The service bulletin is for those who which to install RS-232 using the 1488 quad line driver and 1489 quad line receiver IC. These used to be available at Radio Shack, but not anymore. They forgot about push to talk in their design and so I made a note of what to install. You will need to make your own serial cable if you chose this option. You may have difficulty finding the right female DB-25 board mounted connector to extend out the back of the CP-1. I have a simple solution to the problem. Data sheets for the 1488 and 1489 are available.

A Simple RS-232 Serial Communications Interface for the CP-1

If you use this schematic and wire the RS-232 into the CP-1 as shown, you may use a standard, off the shelf (shielded) serial port cable. As usual, I used what parts I had on hand. Use what ever you want for a +5 Volt stable power source for the MAXIM IC. If using a 7805 +5 Volt regulator, definitely use bypass capacitors on the input and output of the 7805 as shown. This really is the easiest way to go on RS-232 for the CP-1.

DB-25 Connector for CP-1

I have no idea where you can obtain the actual PC board mounted female DB-25 that will extend out past the edge of the CP-1 board. Shown here, I mounted a DB-25 up side down (solder pins facing up), so I could use the existing bolt holes on the board. Note how the connector extends past the board properly now. I soldered wires from the connector pins to the proper holes on the PC board. I had to put a piece of perf board under part of the DB-25 for leveling. Note my RS-232 board on lower left. I used dip headers to plug my board into the empty sockets.

No, the picture does not match the schematic above. Follow the schematic, it's easier!

If the RS-232 factory option is installed
When you have confirmed that the CP-1 does have the RS-232 option installed from factory, there is only one thing left to do. Connect the CP-1 to a PC via a proper serial cable. NOTE: Assuming the RS-232 was installed at the factory, both the AEA CP-1 and CP-100 are not pin for pin compatible with a standard serial cable to the PC if you plan to use DOS modem programs like AN-93 (Terman), SP, BayCom, HamComm, and BMK Multy. Again, it is the unconventional way the modem programs use the serial port. Two choices exist to resolve this issue.

Rewire serial port on modem
One choice is to go inside the modem and rewire the data lines going to the DB-25 connector on the board so that any standard, off the shelf, serial cable can be used. You would only be changing a few lines. I chose this way myself only because my CP-1 did not have RS-232 and so I had to build up everything anyway. There is enough documentation on this site and in the CP-1 manual to accomplish this.

Make your own serial cable
The second choice is to just make your own serial cable. Below is a chart to help you do this. It will work for either the CP-1 or CP-100.

Technical Data

Download CP-1 instruction manual with schematic 2.1MB PDF

Download AEA bulletin/RS-232 modification for CP-1 80K PDF

CP-1 main page

CP-1 tips, tricks, and modifications

Where to purchase the IC's

How to make other TTL to RS-232 interfaces

Data sheets for Maxim, 1488 and 1489 IC's

DOS programs for the AEA CP-1

Oscilloscope Tuning
	The AEA CP-100 and CP-1 has Oscilloscope output for accurate tuning. My favorite feature!

Notice...
You are encouraged to check all of the pages on this web site for the information you seek, starting at the main page. Each page is possibly related to another. The information on each page is "as-is", try at your own risk, and so on. We can help you out some what, as time permits. Try to stay on topic. Please, do not ask to "engineer" or "re-engineer" a design to suit your special project. We do not sell parts or kits of any kind. All said, we are open to any suggestions on adding more material, as long as it is on topic with a particular web page of the Technicothica web site. An example of things that are not "on topic" are: Support for APRS, EMWIN, TNC's and sound card stuff.    ~Thanks!

[ Home | AEA CP-1 | AEA CP-100 | TCM3105 Modem | XR2206 and XR2211 Modem | AM7910 and AM79101 Modem ]
[ TTL to RS-232 Interface | [Data Sheets | Programs for Modems | Part Resources ]
[ What's new | Miscellaneous | F.A.Q. | E-QSL's | E-Mail John - KC4KLM | E-Mail Sam - W4KUM | Our QTH ]