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214 results from messages in altaircomputerclub

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  • Bill, You can't use an ohmmeter to test LEDs, because their resistance is not linear with voltage the way a normal resistor is. So the value that your meter shows will vary wildly with the voltage of your particular meter, and the state of its battery charge. The easiest way to test an LED is to use a 220 ohm resistor to hook it up to a 5V supply. If you don't have a bench supply...
    eberhard@... Apr 25
  • The danged 680 does not have enough slots - if you install a 680-UIO (as I have done) to get another serial port, then you are limited to 32K of RAM - two of their 16K boards. Annoying tradeoff.
    eberhard@... Apr 21
  • I load Basic quite reliably on my 680 - both with a Teletype ASR33 and via a high-speed (9600 baud) paper tape reader, connected to another 680 serial port. (This requires first loading a short loader program via the Teletype.) My Teletype is connected to the 680 via current loop, which has been quite reliable. The ASR33 on that machine is a pretty beat up unit, but the reader is...
    eberhard@... Apr 21
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  • Answer #1 Yes, the 680 motherboard should be set for 2 stop bits. The stop bit setting does not matter when the Teletype is sending data to the 680 (for example, when reading tape), but it matters when the 680 is sending to the Teletype. If there are not enough stop bits when the 680 is sending, then the Teletype will sometimes mess up when printing or punching. Rather than {7 data...
    eberhard@... Mar 28
  • I bet the reason is that you have the Telebyte set up wrong. I bet you have the Receive set up in the "Passive" mode, and it needs to be in the "Active" mode. (Double check that the Transmit is in the "PPassive" mode while you are at it. I think it will work if it is set wrong, but you may damage something after a while that way.)
    eberhard@... Mar 24
  • One more thing... Looking at the Telebyte manual, you need to make sure the Active/Passive switches are set correctly. For the receiver side (receiving from the Teletype), the switch should be set for Active (the Telebyte device provides the loop current). For the transmitter side (sending to the Teletype), this should be set for Passive (the Teletype provides the loop current). In...
    eberhard@... Mar 24
  • Hi Bill, Your description is a little unclear to me. Let me start with a few basics: Normal 8-bit async serial communication has the following components, in this order: 1 start bit 7 or 8 data bits 0 or 1 parity bits 1, 1.5, or 2 stop bits When the line is idle, the level is the same as a stop bit. An ASR33 receives with 1 start bit, 7 data bits, a parity bit (which is ignored...
    eberhard@... Mar 24
  • Josh, I actually did model it with Sketchup to make sure it would all fit, and to get an accurate PC board shape :-) Martin
    eberhard@... Feb 22
  • If anyone's interested, I just ran a new batch of my ME1702/A kits. I am too busy to print the manuals these days, so you can download the manual in pdf form here: ME1702A You will find the bill of materials for the components that you'll need to order from Digikey and Allied Electronics in the appendices at the end of the manual. (You will also find the firmware source code in...
    eberhard@... Jan 19
  • I also use USB serial port adapters - in my case, plugged into a MacBook, which is running XP in a virtual machine. No problems... I suspect the problem is with your RS232 receiver chip circuit, the DM1489. Note that pins 2, 5, 9, and 12 of this chip connect each to a control resistor, which can shift the switching threshold voltage of the receiver. I suspect that the particular...
    eberhard@... Jan 16