Troubleshooting keyboard input in replica 1 TE

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Troubleshooting keyboard input in replica 1 TE

Postby rookie2013 » Oct Sun 13, 2013 10:19 am

Hello folks,

I'm having some trouble with what I believe is the I/O part of my replica 1 TE. Maybe someone could please give me tips on how to troubleshoot it.
Sorry for the long post, but wanted to give as many relevant facts as I can up-front. Here are the symptoms:

When I power up my replica 1 and both reset the processor and clear screen, I get a backslash plus a line feed and a carry return
(the @ cursor goes down to the next line on the screen).
I think this is happening at what seems to be a pretty constant rate of about 3 seconds.

So, for example the first thing I see is:


After about 3 seconds I see:


And so on. When I type on the keyboard, nothing else appears on the monitor screen. I get the same thing. So the replica 1 is not responding to the keyboard.

I have done some troubleshooting. I placed my voltmeter on pin 12 of the ASCII port on the replica 1 and typed a few keys on the Apple II+ keyboard I have. I see the voltage there going from low to high and from high to low, depending on what keys I press. Then I do the same on pin 2 of the 6821, and unfortunately I don’t see any changes in voltage. The continuity checks I do between the ASCII port pins and the pins of the 74LS245 are all good (same thing between 74LS245 and Propeller), so I am thinking that the problem may be located somewhere in between the 74LS245 and the 6821 chips. I have replaced both the 74LS245 and the Propeller chips with fresh ones, and nothing different happens.

1) I did not install the PS/2 keyboard port and its associated components, not the RS232 port and its associated components, not the expansion ports on my replica 1 yet. I just want the basics to work first (CPU, Memory, and keyboard/video I/O). I don’t have a need for those now. Also, I don’t have a PS/2 keyboard to use.

2) I have two Apple II+ keyboards, and the same thing happens no matter which one I use.

Thank you folks for any pointers or tips you could provide.

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Joined: Oct Tue 08, 2013 7:58 pm

Re: Troubleshooting keyboard input in replica 1 TE

Postby rookie2013 » Dec Sun 01, 2013 5:03 pm


This issue has been resolved.

It seems that, in order to use the replica 1 TE, you need to install the MAX232 dual EIA-232 driver/receiver chip (and also install the five associated 10 uF capacitors and 1K resistor), even if you do not plan to use serial ports at all.

From what I can see, the Propeller chip requires the TX and RX circuit (pins 39 and 40 respectively) which includes the MAX232 chip to be completed in order to operate properly. I haven't look at the source code of the Propeller, but will do so later to see if I can figure it out.

Vince, I am curious, why is this the case?

Thanks to all for your help.


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Joined: Oct Tue 08, 2013 7:58 pm

Re: Troubleshooting keyboard input in replica 1 TE

Postby vbriel » Dec Mon 02, 2013 6:10 pm

On the TE, the max233 is integrated with the keyboard input design and I used a latch so you could use both at the same time. This creates a scenario where you must use the max232 and the latch for the circuit to function correctly. What I like is the plug and play so to speak simplicity that you can use both keyboards at once, or either one when you want. What it created was an extra chip with the latch. In my anniversary edition I added a jumper (which I hate jumpers) but now I can turn off the ASCII keyboard even if plugged in. Without a way to disable the ASCII keyboard you get a shadow character of the last ASCII character you typed after every new character on the PS/2 keyboard.

So, long story short, the design is set up so you can use both keyboards at once but you have to install all the IC's for it to work, otherwise the reading of the Rx port is reading garbage and hogging the keyboard bus. Hope this clear things up. By the way, you are the first to mention notice of this!

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