LK5R - The Seventh Link

[Bryce]

Hi all,
     I was looking through a few cartridge PCBs I have here and I noticed that some cartridge PCBs have an extra link called LK5R, positioned between LK5 and the ACIDs capacitor. This isn't mentioned on the Wiki page at all (although it can be seen in one of the PCB photos). Did any cartridge ever use it? It does the opposite to LK5. LK5 straps pin 3 of the EPOM to the 5V line, LK5R straps pin 3 to GND.

Bryce.

[Kris]

I have never seen this LK5R wired up to now............What is the function to link pin 3 of the Eprom to Gnd ?

[Bryce]

On 32pin EPROMs it's A15. The only use I can think of would maybe to use 28pin EPROMs in the cartridge?

Bryce.

[Badstarr]

A relic from an earlier design perhaps ? Or maybe something utilised on the GX4000 demonstraition system?

[Bryce]

More likely a cost factor - Where "Only use a 64K EPROM if the game fits on it" turned into "It's cheaper to buy half a million 128K chips than buying 250 thousand of each type".

Bryce.

[TFM]

Half a million? Where are all that carts? Damn, my cart secret service suxx! 

[Bryce]

Half a million? Where are all that carts? Damn, my cart secret service suxx! 

Yeah, I was a bit generous with that example, but it was the theory that I wanted to point out.

Bryce.

[The Last Bandit]

Out of curiosity, what sort of volumes are needed before masked ROMs are more cost effective ?

[Bryce]

No idea. That sort of thing ended while I was still in university OTPs are used these days, if at all. Everything's flash now.

Bryce.

[ralferoo]

Out of curiosity, what sort of volumes are needed before masked ROMs are more cost effective ?

I got the impression that it was tens of thousands back in the 80s. There was also the factor that the lead time could be 3-4 weeks.

A mask ROM isn't all that complicated, much like a ULA isn't all that complicated to specialise. It's not something you or I could do, but the process is taking a stock unprogammed ROM or ULA chip and applying a fixed metal mask on top of that that joins up the silicon areas in the correct way.

So, they'd have a large inventory of the unprogrammed parts and then there'd be a lead time and cost associated with making the design for the metal mask, but after that it's cheap and easy to produce.

[MacDeath]

still if only Amstrad actually bought a stack of 256K ROMs...

[TFM]

You mean very cheap 512 KB types and good coders too