Numpty alert. SN74LS379N IC replacement

[UKRetrogamer]

I have an EPROM cart which I bought some time ago which had a SN74LS379N IC placed in a socket. The socket was too close to the front of the board and as a result, could not be cased unless the socket was removed to give vertical clearance for the llid. I've noticed other Ti EPROM carts I own also have the same IC.

I removed the socket and soldered the IC directly onto the board, checking for available clearance. Yup, the case now fits.

Unfortunately (and being a complete numpty) I didn't check the orientation before soldering the frickin' IC into the board uʍop ǝpısdn!

Despite having a desoldering gun, I ended up having to CUT the chip off the board. (Soldering skills 8 out of 10, de-soldering skills 2)

I've checked online and apparently the exact IC replacement from Ti is an obsolete product.

The only part I can find on UK eBay lacks the second S in the part no. SN74L379N as opposed to SN74LS379N. Will this part work as a replacement for the (now legless) IC I removed?

This is the part I found:

http://www.ebay.co.uk/itm/250531689108

Edit: Part No. in item description, highlighted in Red excludes the second S. The title shows the part no. with the S but excludes the prefix SN; hardly surprising I don't know what I'm looking at.

Confirmation required the part above will work as a replacement.

Edited November 10, 2014 by UKRetrogamer

[Stuart]

If you want to drop me your address in a PM, I've got several spares of those and you can have one.

 

Stuart.

[+Ksarul]

You definitely need the LS version of the chip, although you could replace it with an HCT variant (although I'm not sure if they ever did an HCT variant of the 379s).

 

I tend to keep several hundred of them on hand for the boards I build, so they are always available within the community if Stuart doesn't have any (I bought 250 of them this past weekend because I was running low).

 

Which EPROM board are you looking at? The only one that had the socket too close to the case from the ones Jon did were the 16K boards. . .and all of mine are set to ensure sufficient clearance.

[UKRetrogamer]

That's the board (I think). It also has solder on the edge-connector pins to increase their thickness. I use it solely for the 16K TurboForth ROM. There are no jumpers on the board, so it's only of use for this or other 16K EPROMs.

 

I tried to encase it the other day but found the case wouldn't close so I decided to remove the socket as I could see there would be enough clearance if I mounted the IC directly to the board.

 

That's where things went pear-shaped.

 

I've found some with the correct part number online. I've ordered a couple just in case I make the same mistake again.

[UKRetrogamer]

It's working again. Having replaced the IC with another of the same type and soldering it into place in the correct orientation this time around, I now have a working EPROM cart again (along with 3 spare ICs).

 

What's the difference between a 74LS379 (as used in the 16K ROM cart) and the 74LS378 used in the 512K cart?

[Omega-TI]

 

What's the difference between a 74LS379 (as used in the 16K ROM cart) and the 74LS378 used in the 512K cart?

 

Damn good question. They are also on the same datasheet.

I think it's the number of registers.

 

 

[UKRetrogamer]

 

Damn good question. They are also on the same datasheet.

I think it's the number of registers.

I was wondering if the spares I now have could be used in both 16K and 512K carts but looking at the datasheets, apparently not. However, the 64K hexbus cartridge board I have, also uses a 379 and it made me wonder why the 512K boards use a 378.

[Stuart]

'378 is 6 latches, '379 is only 4 latches.

[+Lee Stewart]

Bank selection with 379 quad latches is inverted and for 378s {EDIT: 6 latches} is not. For 379s, bank 0 is always the highest possible bank address in the ROM. For a 2-bank ROM, writing to 6002h selects bank 0 and 6000h selects bank 1. For a 4-bank ROM, it's 6006h:bank 0, 6004h:bank 1, 6002h:bank 2 and 6000h:bank 3. All you need to do to use a 378 in place of a 379 is to invert the order of the 8KB banks in the binary before burning the EPROM—pretty simple to do with a hex editor. {EDIT: Based on Stuart's info, it does not look like you can substitute one chip for the other without changes in circuitry! You can, however, do the bank inversion if changing from a board with a 379 to one with a 378, as long as the EPROM size is the same.}

 

...lee

Edited November 11, 2014 by Lee Stewart

[UKRetrogamer]

That's useful to know. Rasmus wrote a Java ROM Bank-inverter applet which I've used before for this very purpose. It's floating around on the Ti-99 programming forum somewhere.

 

Edit: Bah. You gave with one hand and took with the other. *grumble*

Edited November 11, 2014 by UKRetrogamer

[+Lee Stewart]

That's useful to know. Rasmus wrote a Java ROM Bank-inverter applet which I've used before for this very purpose. It's floating around on the Ti-99 programming forum somewhere.

 

Edit: Bah. You gave with one hand and took with the other. *grumble*

 

I blindly assumed (always a bad idea ) that a 379 could only be used for inverted bank selections since I had never seen one used any other way. It actually can be used either way because the chip has both outputs! If my simple-minded way of looking at it is correct, you would only need to cut 3 traces on a 64KB board and wire them to their un-inverted counterparts on the chip.

 

..lee

[+Ksarul]

You are correct. Lee. . .and it is a four-trace change on the 128K boards.