On 07/13/2016 07:12 PM, Jim Brain wrote: > On 7/13/2016 11:30 AM, smf wrote: >> On 13/07/2016 13:48, Gerrit Heitsch wrote: >> >>> In man circuits they control the EPROM through _OE and tie _CE to GND >>> since that allows you to get away with slower EPROMs. This way the >>> EPROM is always aktive and decoding addresses, just the output >>> buffers are disabled. So you can hide quite a bit of the access time >>> inside the delay for the decoder that selects the EPROM. Downside: >>> higher power consumption with the old NMOS types. Doesn't really >>> matter with CMOS. >> >> Exactly, which is why I suggested hooking up to _CE and using a >> buffer. I am assuming that anything with a 2364 pinout is going to be >> the same speed or slower than something with a 2764 pinout. > I think you have it backwards. the OP wants to put a 2364 into a 2764 > socket, so the 2364 could be much slower than the original socket expects. >> >> If the 2364 you are using is actually powered up all the time decoding >> addresses and the _CE only turns on the output buffers > _CE does not turn on output buffers. _CE is chip select. _OE turns on > output buffers Yes, but somewhere in a Commodore datasheet I read that that the 23xx ROMs didn't really have a power down, so they really might have had the ROM running all the time and using _CE to only control the output buffer. The datasheet mentioned their 24xxx ROMs being able to power down. It's here, search for '24128' http://www.zimmers.net/anonftp/pub/cbm/documents/chipdata/csg.chips.info >> then you could get away with just checking for (_CE | _OR ) == 0. > You can do so, but that costs an OR gate, and most times, 2764 sockets > just tied CE to ground all the time, as the power savings with CE =1 > would not matter. With NMOS-ROMs it makes quite a bit of a difference. Replacing the 16KB NMOS ROMs in a Commodore C16 or +4 with a 27C128 each results in power savings of 50mA per Chip. 2 ROMs = 500mW power savings. > If you > deadbug the IC, you can stash it in the interior of the 24 pin socket, > as you only need 5 connections (A,B,Y,PWR,GND) Well, you should not leave unused inputs open. Some logic families don't like that. Gerrit Message was sent through the cbm-hackers mailing listReceived on 2016-07-13 18:00:33
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