| Posted by Steve L. | June 24, 2018 - 03:46 pm |
| Hi Andi8086 and thank you for the interesting question! The answer lies in the fact that the Vgg pin of the 1702A is expected to source current during the programming. The programmer hardware only needs to pull it down or let it go to the +47V rail. Since the specs require that it only be pulled down to about +10V, the Zener is placed in series with the pull-down driver, Q1. I will be happy to help if you have any other questions. |
| Posted by Andi8086 | June 24, 2018 - 01:23 pm |
| Hi, I don't understand the Zener Diode in your circuit. The forward voltage usually is around 0.3 Volts or so, which means, that you get 46.7 Volts on VGG. Okay so far, but how do you get 10 Volts... there is nothing connected to the pin anymore if the Diode blocks, i.e. Ground on one side and the pin on the other side. Is it with remaining charge on Vgg itself? |
| Posted by VA3QE | May 03, 2017 - 08:12 am |
| Thanks. That saves me a lot of time drawing it out from scratch. |
| Posted by Steve L. | May 02, 2017 - 08:47 am |
| Hi Va3qe, You can download the Eagle schematic here: http://www.tronola.com/misc/1702A_Programmer_Board.sch You may use it as you wish; I would only ask for proper attribution, where due. |
| Posted by Va3qe | May 02, 2017 - 08:12 am |
| Did you do the schematics in Eagle? If so can you post the eagle files? |
| Posted by Steve L. | August 30, 2014 - 02:46 pm |
| Hi Minime, I take it that you meant to say "reader part" at the end of your message. Yes indeed, to extract the reader part, look at the sections enclosed in dotted lines at the lower left of the schematic. (Unfortunately for clarity, the DB25 connectors are also drawn with dotted lines but please ignore those for the moment.) The dotted lines I mean are labeled "Optional Reader" and "Optional Reader Pwr Ctrl." To make a reader, you need what is contained in those two sections, along with the DB25F connector directly above. Then make the separate adapter cable shown on the left. The adapter cable goes from the reader board to the two parallel ports needed on your PC. Beware that many newer PCs don't have parallel ports. Only the +5V and -9V power supplies shown in the dotted lines are needed for the reader. If you are careful to keep those supplies off when inserting and removing the 1702A, you could leave out the "Optional Reader Pwr Ctrl" section. In that case, about the only things left on the reader board would be the 1702A socket, a couple caps and the DB25F connector. No active electronics needed! I don't know of any reason why the existing software wouldn't work with this arrangement. Of course, the only useable command will be (R)ead. Choosing that will prompt you for a filename and a choice of ASCII or binary format. It will then read the PROM data and put it in the file. I wish you the best of luck with your project. |