Z80 Telescope Controller (was Homebrew newsgroups / forums?)

Allison ajp166 at bellatlantic.net
Thu Oct 27 06:53:31 CDT 2005


>
>Subject: Z80 Telescope Controller (was Homebrew newsgroups / forums?)
>   From: gtulloch at shaw.ca
>   Date: Wed, 26 Oct 2005 23:36:51 -0500
>     To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at classiccmp.org>
>
>Well, ok, in that case ...
>
>I'm building a Z80 based microcontroller as a telescope controller, to 
>run a few stepper motors, calculate and correct for periodic errors as 
>well as XYZ errors in the mount. The driver circuit is done 
>(http://www.bbastrodesigns.com/cot/steppercircuit.html), and 
>currently runs off a DOS app which uses the parallel port to pulse 
>the motor windings. However, I prefer not to use a dedicated
>DOS PC so I'd like to put a Z80 in front of the driver with an RC 
>circuit connected to the NMI so I know how long the duration between 
>interrupts is and can thus calc the steps required to track. For historic
>reasons the code will be written in FORTH - a PC connected via serial
>will do all the heavy lifting as far as telling the Z80 where to point 
>and how. Comments on the veracity of this architecture welcome!

RC circuits drift with temerature and voltage, not an accurate source of
time or position information.  A better whay uses a timer chip like the 
Z80 CTC or 8253.  Though a PIC or other micro(8048, 8051) usually has a 
timer counter on board.

Generally speaking using a micro as a morot controller is commmonplace.
The real trick is being able to start at a calibrated point and return
back to it (resetability) as well as move to any point with accuracy.
So beside the mechanical problem of movement there are the issues of
knowing where you are or at least where the start point is.

>I have a few questions I'm hoping someone can answer for me, starting 
>with the following: I have a Z80A and a 4 mhz TTL clock 
>oscillator - I'm wondering if it would be ok to connect the clock 
>directly to the CPU or is it wise to connect it via a parallel or 
>serial resonant oscillator circuit like those described here:

Yes, you can if CMOS, if not then add a 330 ohm pullup resistor.
The Z80 requires a clock that swings closer to ground and Vcc
than all the other pins.

>http://www.z80.info/uexosc.htm
>
>Why be so elaborate? The data sheets for the oscillator doesn't say 
>"Make sure you connect via a parallel or serial resonent oscillator 
>circuit!" 

Because most digital hackers would not know what it is maybe?
A parallel or series resonant osc refers to the whay the crystal is 
connected in and used.  The inportant thing is to meet the rise and fall
times as well as the logic high and low voltages that the Z80 requires.
and that wasn't addressed well there.

>Thanks for any light you can shed on this, Google hasn't been helpful.
>I have references that do it both ways without explanation so I'm 
>confused!

If google isn't helpful then you asked the wrong question.  There is literally 
mountains of z80 information out there.


Allison



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