HYDRA Keyboard Configuration ?

RonP

Hello All,

I got a dumb question for you all. The Hydra from what I can understand uses 4 pins for the keyboard and 4 for the mouse and it explains why. Can I use the Hydra with Embedded Basic (for example) so I can save my little programs instead of using the Demo Board where I can't save them.

The Hydra uses Pins 12, 13, 14, 15 for the keyboard I think, 13 is data and 15 being the clock.
In the code snippet below from Embedded Basic could I just use 13 data and 15 clk and be OK. And forget about Pins 12, 14. Or is there a lot more I need to do? I don't just want to plug in the numbers and try it for fear of messing something up.

PS2Dat      PIN 26 INPUT ' 26 for demo board, 10 for Dongle
PS2Clk      PIN 27 INPUT ' 27 for demo board, 11 for Dongle

Sorry if the answer is obvious I am having a hard time figuring this out.:blank:

AndreL

You are definitely not going to hurt anything, so don't worry about that. The reason the HYDRA uses 4 pins for keyboard and mouse is that Chip was really worried initially about hooking 5V to the Prop and buffered them with transistors, thus I usually only use 2 lines for PS/2, but he used 4 and rather go against that design, I used what Chip felt comfortable and Parallax at that point in time, but of course, now everyone is pumping 5V into the Prop with resistors or dividers and 2 pin PS/2 ports are the norm.

That said, you have to use the 4 pin drivers for mouse and keyboard and waste 4 pins. However, no one says you can't hot wire a couple signals and turn the HYDRA PS/2 ports back into 2-pin, let me look at the schematic a second here...Ahha! It can be done very easily. Ok, looking at the schematic of the PS/2 connectors (I can't attach it? so look in your hydra book/cd) -- do this:

1. Remove Q1, Q2, Q3, Q4 - this breaks all the pull down circuits and frees up P8, P10, P12, P14.
2. Give that a try as is with the Mouse on pins (9,11) for data, clock and the keyboard on pins (13,15) for data, clock.
3. If that doesn't work then swap R10 (22K) <---> R11 (2.2K), and R13 (22K) <--> R14(2.2K)
4. If that doesn't work then after the swap replace R11 (2.2k) and R14 (2.2k) with 100-330 ohms.

Basically, pulling Q1..4, makes the circuits just like all the 2-signal PS/2 ports, then we are just trying to minimize how many resistor changes we make since I like using a 100 for the drive resistor off each data/clock and a 10K pullup. But, we can try the 2.2 and 22K and see if they work to save soldering.

But, that's it!!! Find what works, write it up, post a modified schematic and this take 5-10 mins and people can free up 4 pins and use the new 2-pin PS/2 drivers.

Andre

RonP

Andre,

Thanks for the detailed explanation. I think I might give it a go. It would be nice to be able to use the 2-pin drivers.

-Ron