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74HC74 sega master system1 switchless trouble.

Started by bigsanta, August 24, 2010, 01:13:37 pm

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bigsanta


I've tried connecting up a 74HC74 ic to my sms 1 ,using part of simonbelmont2's mega drive guide below.My sms1 is a UK pal version,with the 3 solder pads ,left is ntsc(ground), centre is the signal and right is  pal(+5v) and i've cut the underside linking trace, between pal and signal.

My connections to the 74HC74 are like this;

SMS NTSC solder pad(gnd)to pin 7 (gnd)
SMS PAL  solder pad (+5v) to pin 14,1,4 (Vcc)(1R'd)(1S'd)
SMS SIGNAL solder pad to pin 5 (1Q)
74HC74 pin 6 (Q')  to pin 2 (1D) of 74HC74
74HC74 pin 3 (Q) to the SMS's IC 315-5216  pin 22 reset http://emudocs.org/Master%20System/master.gif

Now when i power on,the sms 1 is in ntsc mode ,but when i press the reset button,there is no switching to pal mode ,just a system reset takes place.

Any pointers to what i've done wrong ?


http://nfggames.com/forum2/index.php?topic=3789.0

albino_vulpix

Are your LEDs set up? If so, does pressing the reset button rapidly change the LED status?

bigsanta

August 25, 2010, 12:00:12 pm #2 Last Edit: August 25, 2010, 12:13:36 pm by bigsanta
Quote from: albino_vulpix on August 24, 2010, 07:11:09 pm
Are your LEDs set up? If so, does pressing the reset button rapidly change the LED status?


At the time,i left the LED off,but today i tried connecting up my bi-colour LED .It's 3 legs have the middle one as the anode and the outer legs are  cathodes,so i assume this is a common anode LED ?

Well i couldn't get it to light up red then green,just 1 colour for one region and off for the other and i'm stumped with how you would connect it to work properly.

So i switched to two separate LEDs ,and connected  PIN 5 Q to the SMS signal pad and also to a POT which is set to 400 ohms.This is then connected to LED 1's anode and to LED2's cathode. Then Q' to LED 1's cathode and LED 2' anode ,as per the picture (this is all on a breadboard )!

When i press reset,there's no rapid changing of the LEDs,what happens is this. LED 1 will be on when i switch on the sms and it will be in PAL mode,I can hold the reset button for half   a second ,the sms will reset and LED 1 will stay lit,but when i let go of reset , LED 1 will go out and LED 2 will come on and the sms will be in NTSC mode.Now if i try the same thing again, sometimes it will do the same and revert back to PAL,but other times the LED will switch off as soon as i touch reset (now both LEDs are off)and after  half a second i release the reset button ,and the LED that went off,comes back on and it's still in the original country mode it was in. This has happened 3 and more time in a row before it corrected itself .

Other times i have to tap the reset button,another time ,if i hold the rest button too long,the sms will reset to a black screen and needs switching off then on.There has never been an outcome like  what you see in any of the switchless video's,where you hold the button for a time and the LED switches colour to show you it's in the new mode and you can release the button.This just doesn't happen for me.  

Just to be thorough ,this is an 74HC74N and i'm only using 1 flip flop which i assume is correct for only having one output signal with an sms ,unlike the 2 outputs which the mega drive needs .

If i left the sms out of the connection and just prototyped the circuit on my breadboard,would the LEDs toggle on and off  with a set time between each high low status ?

 


albino_vulpix

Quote from: bigsanta on August 25, 2010, 12:00:12 pm
Quote from: albino_vulpix on August 24, 2010, 07:11:09 pm
Are your LEDs set up? If so, does pressing the reset button rapidly change the LED status?


At the time,i left the LED off,but today i tried connecting up my bi-colour LED .It's 3 legs have the middle one as the anode and the outer legs are  cathodes,so i assume this is a common anode LED ?

Well i couldn't get it to light up red then green,just 1 colour for one region and off for the other and i'm stumped with how you would connect it to work properly.

That suggests the flip-flop is working properly.

So i switched to two separate LEDs ,and connected  PIN 5 Q to the SMS signal pad and also to a POT which is set to 400 ohms.This is then connected to LED 1's anode and to LED2's cathode. Then Q' to LED 1's cathode and LED 2' anode ,as per the picture (this is all on a breadboard )!

The way that circuit is set up, you're best to use 2 individual LEDs.

When i press reset,there's no rapid changing of the LEDs,what happens is this. LED 1 will be on when i switch on the sms and it will be in PAL mode,I can hold the reset button for half   a second ,the sms will reset and LED 1 will stay lit,but when i let go of reset , LED 1 will go out and LED 2 will come on and the sms will be in NTSC mode.Now if i try the same thing again, sometimes it will do the same and revert back to PAL,but other times the LED will switch off as soon as i touch reset (now both LEDs are off)and after  half a second i release the reset button ,and the LED that went off,comes back on and it's still in the original country mode it was in. This has happened 3 and more time in a row before it corrected itself .

Other times i have to tap the reset button,another time ,if i hold the rest button too long,the sms will reset to a black screen and needs switching off then on.There has never been an outcome like  what you see in any of the switchless video's,where you hold the button for a time and the LED switches colour to show you it's in the new mode and you can release the button.This just doesn't happen for me.  

Just to be thorough ,this is an 74HC74N and i'm only using 1 flip flop which i assume is correct for only having one output signal with an sms ,unlike the 2 outputs which the mega drive needs .

That's right.

If i left the sms out of the connection and just prototyped the circuit on my breadboard,would the LEDs toggle on and off  with a set time between each high low status ?



I had a similar issue when I was using flip-flops in my NeoGeo -> Master System converter. Turnes out it was simply a bad connection on the breadboard! Worked fine when it was soldered together. Have a photo of your setup?

bigsanta


bigsanta

August 25, 2010, 01:46:51 pm #5 Last Edit: August 25, 2010, 02:10:54 pm by bigsanta


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I removed the gnd , +5v and signal wires from the sms solder pads and just used other locations .Also ignore the wire coming from the reset button terminal.

albino_vulpix

Maybe you need to tie the unused inputs (set, clear, clock, D) on the second flip flop high/low, since it's a CMOS device? Could cause things to act funny.

bigsanta

Quote from: albino_vulpix on August 25, 2010, 02:16:10 pm
Maybe you need to tie the unused inputs (set, clear, clock, D) on the second flip flop high/low, since it's a CMOS device? Could cause things to act funny.


Even that didn't work albino_vulpix ,but i've just remembered one vital thing.As you can see,my breadboard is one of those 300 in 1 malarkys , it's been a while since i last used the thing,but i remember in one of the IC tutorials i tried,the circuit didn't work for some reason and the reason being,if the IC's weren't kept firmly pressed into the breadboards terminal holes ,then the pins down the whole of 1 side of the IC wouldn't actually be connected to the board properly,so we had an open circuit.

And i've just quickly tested this now with the 74HC74 and it's the same problem happening.So it looks like it's all down to this breadboard :'( >:(

So, what you you said about your faulty breadboard,holds true.

bigsanta


albino_vulpix

So you soldered it together and it still acts the same? As in it'll start in NTSC, then sometimes go to PAL with the button press? WHat do the LEDs do?

bigsanta

Without using an IC ,instead, constructing a transistorised toggle flip-flop circuit on mybreadboard,with NTSC wire as the 0 Vss ,PAL wire as Vcc +5v and the SMS signal wire connected to the LED's anode ,i get perfect toggling between 50/60 hz speed .

Taking the sms out of the circuit and just using cells as my breadboard power supply,the LED toggles on and off as normal,something which just doesn't happen with the other 74HC74N circuit, faulty IC's ?

albino_vulpix

August 29, 2010, 09:13:03 pm #11 Last Edit: August 29, 2010, 09:14:43 pm by albino_vulpix
Could be a damaged IC. Having floating inputs might have done that, since it's a CMOS. If you want, give this one a try. It uses a J!K flip flop (just a regular flip-flop, with K inverted), and it of the LS family, so floating inputs aren't an issue. Forgive the rush Paint job :p
Also, if the second LED is showing up as "Q2" (probably something to do with nfggames' cache, the direct link should work), it means "!Q1"