74HCT 688 for CT-Flash(jumpstarter)

dodo · Fri Jul 25, 2003 8:31 am

I want to build CT-Flash, and I have difficulty to find 74HCT688 in local shop.

The dealer offered me 74HC688 instead of 74HCT688.
I asked what is the different the two of them. He said only the speed.

if I not mistaken, writing BIOS need proper timing because of sequential.
If I installed 74HC688, Can this device working well?

Fri Jul 25, 2003 11:02 am

It should work without any problems. I have 74LS574 instead of 74HCT574 and it works fine. The biggest difference is that 74LS is more expensive

When repairing some boards, I often replaced 74F with 74LS or even 74HCT because some of them were not available in SMD or even not available at all - and it works.

dodo · Sat Jul 26, 2003 5:36 am

>I often replaced 74F with 74LS or even 74HCT

what do you mean replaced 74F.

AFAIK it is 74HCT in bill material not 74F <http://www.heise.de/ct/Redaktion/ea/fla ... asheng.htm>

does 74F better than 74LS or 74HCT?

what are the difference among them?

Sat Jul 26, 2003 11:39 am

There are 74xxx, 74HCTxxx, 74HCxxx, 74LSxxx, 74Fxxx. 74Fxxx are "the best" - they're fastest (it means that they can work at highest frequency. 74HC and 74HCT are almost same - 74HCT needs 4,5V to 5,5V to operate, 74HC should work from 2V to 6V.
You can use any of these on an ISA card - because even the slowest one (74xxx) is fast enough for that.

sulbert · Fri Aug 01, 2003 9:51 pm

Replaced the 74HCT574 chip of my c't-flasher with a 74HC574 one. Result: c't-flasher is not recognized by the software anymore. AFAIK 74HCT has TTL switching levels but 74HC has half supply switching. Of course there is always a possibility that the 74HC chip is bad (unfortunately no possibility to test it).

dodo · Sat Aug 09, 2003 7:04 pm

Hello sulbert!

I thank you for your reply, Can you tell me more?

I would like to know every 74xxx chip you use for your CT-flasher.
How do you build yours, using eMedia PCB or pre-assembled kit?

today, does your CT-Flasher work correctly?

74HCT688 => I can't obtain this one, how yours?
74HCT245 =>i can obtain it , how yours?
74HCT32 =>i can obtain it , how yours?
74HCT02 =>i can obtain it , how yours?
74HCT574 =>i can obtain it , how yours?

sulbert · Wed Aug 13, 2003 9:48 pm

dodo wrote:How do you build yours, using eMedia PCB or pre-assembled kit?

I ordered the PCB from eMedia a few years ago and bought the 74HCT chips and passives from a local electronics shop. Pre-assembled kit would be just too uninteresting (and also a bit expensive) for me

dodo wrote: today, does your CT-Flasher work correctly?

Yes

I have managed to destroy it a few times because of various experiments with different adapters and onboard flashing.

dodo wrote: 74HCT688 => I can't obtain this one, how yours?
74HCT245 =>i can obtain it , how yours?
74HCT32 =>i can obtain it , how yours?
74HCT02 =>i can obtain it , how yours?
74HCT574 =>i can obtain it , how yours?

I could get all the chips. For 688 I had to wait a few days (if I remember correctly).