Minimig Discussion Forum

Hi,
this weekend i made a port of the zxgate Spectrum core
http://zxgate.cvs.sourceforge.net/viewvc/zxgate/
for the Minimig board.It does not run with the correct clock speed
so it could be possible that tape loading doesn´t work.
Tape input is connected to joystickport 2 Pin 9 (Fire2), sound output is also connected.

Thanks Dirk!
I wanted to do this myself some time ago, but it was a bit too hard for me
Since I dont have any spectrum tape, it just will be for fun.
But its nice to have another alternative core for the Minimig board.

Just tested:
The core seems not to support PAL screen output, right?
Also my LCD screen (Samsung SyncMaster 940BF) just show a garbage screen like some totally unsupported frequency.
I will try this core on a CRT too but it would be great to have at least some close to standard VGA (31KHz 50/60Hz refresh rate) or even a 50/60Hz 15KHz (PAL/NTSC) output as well

The problem is the same like with FPGA64. I can´t set the correct clock speed.
My Eizo CRT shows 51.5 HZ and 32.1 KHz.
It seems the Minimig board is not useable for other cores unless someone has an idea
for other clock speeds-

What clock frequency do you need?

For the spectrum core i need 28 MHz.

Using one DCM with 19/3 multiply rate you get 4.433619 * 19/3 = 28.079587 MHz (+0.3%).
Using two cascaded DCMs with total 120/19 multiply rate (e.g. one DCM configured as 30/19 and another as 4/1) you get 4.433619 * 120/19 = 28.001804 MHz (+64ppm).

With 19/3 rate the DCM works. With it the core has 50.3 Hz 31.3 Khz .
The 2nd version with two cascaded DCMs doesn´t work because the output clock with 7 MHz is to low for the DCM.

You are right, it would work on a Spartan-3E (FCLKOUT_MIN = 5 MHz) but not on a Spartan-3 (FCLKOUT_MIN = 18 MHz).
Fortunately there is very simple solution: configure the first DCM with 8/1 multiply rate (fclkout = 35.468952 MHz) and the second one with 15/19 (fclkout = 28.001804 MHz). It should work, please try it.

Yes, it works.fH: 31.2 KHz fV 50.1 Hz But now the next problem occured. Tape loading via Joystickport still doesn´t work. I have connected the headphone output to joystickport 2 Pin 9 (Fire2) .
I can see the fpga port received something but no audio signals. While loading the border of the screen flashes sometimes.
The Joystickport has a 270 Ohm serial resistor. The same configuration with 47 Ohm resistor works on my DE1 Board.
I tried the User0 on Spare IO with 47 OHM resistor but still no loading.
What are the differences between Spartan 3 and Cyclone 2 IO ports ? Do i need a simple transistor amplifier ?

First make sure you have disabled internal pull-up on that pin. Then try to bias it to 1.4V (e.g. 1K resistor to ground and 2.7K to +5V). Also a capacitor of a few uF in serie with the input signal is highly recommended (or mandatory if the headphone output doesn't have any).