TF330 Bus Switches SN74CB3T3245PW

[terriblefire]

At exxos's request i have measured some bits of the TF330 system to check to see if I can replicate his issues.

The chip in use here is the SN74CB3T3245PW

https://uk.rs-online.com/web/p/bus-switches/6631685

First I measured the lowest data bus pin D0 on the 3.3v side

tf330_bus buffers.JPG (50.58 KiB) Viewed 4489 times

I tried to trigger this at 3,6V just to see if i was being lucky and only seeing reads from RAM.. Nada. Never more than this.

I then repeated these steps at D31 on the 3.3v side.

tf330_bus buffers2.JPG (47.68 KiB) Viewed 4489 times

Finally just to check there wasnt a huge voltage drop across the risers i measured at the 5v side

5v_side.JPG (56.7 KiB) Viewed 4489 times

No issues as far as i can see.

[exxos]

What's going on with the last image, looks like 3v & 5v ?

[terriblefire]

What's going on with the last image, looks like 3v & 5v ?

Yes. Measured on the 5V side. The bus buffers and CPLD are outputting 3.3v. The CPU and Amiga are outputting 5v.

[exxos]

Ahh gotcha.

Thanks for doing the test. I'm clueless why they don't work for me. Not only that, even 3 brands and different chips don't work. Only descrete mosfets and the NXP chips have worked so far.

I did half wonder if it was a power up issue. I saw somewhere some chips have to be powered up or down in a special way. But didn't look into it, as if that was the case they be dead on your board anyway.

I cant see all the chips I tested being faulty from new... Did you get yours from rs ? I got mine from farnell I think..

Icky and myself were trying to get a reset chip to work the other day and we gave up and used a different chip and we are running OK now. So its not just me having issues with chips..

[terriblefire]

I cant see all the chips I tested being faulty from new... Did you get yours from rs ? I got mine from farnell I think..

RS. They deliver so quickly for me i never use anyone else. I get free shipping too.

Icky and myself were trying to get a reset chip to work the other day and we gave up and used a different chip and we are running OK now. So its not just me having issues with chips..

I have no pull ups on the 3.3v side. Are you powering the buffers at 3.3v?

[exxos]

I will get a couple from rs and see if they work..

I've tried everything with those idt chips... All combinations of everything known to man. They just don't work. Theres no real difference with the NXP chips, they work first time as expected, so its not like I'm screwing something up...

[supaduper]

@ EXXOS, bought those Bus Switches here for the TF330

https://www.digikey.co.uk/product-detai ... -ND/770579

[exxos]

@ EXXOS, bought those Bus Switches here for the TF330

https://www.digikey.co.uk/product-detai ... -ND/770579

Thanks.. I might have got them from mouser.. I'm not at home to check ...

Me and digikey fell out a long time ago. I had never ending issues with them

[supaduper]

exxos, Email me your address and I will send you a couple

[exxos]

exxos, Email me your address and I will send you a couple

Very kind thanks. Will do later