On 05/14/2012 06:02 PM, MikeS wrote: > ----- Original Message ----- From: "Gerrit Heitsch" > <email@example.com> > Sent: Monday, May 14, 2012 6:56 AM > >> As for the ROMs... you could desolder all of them, and add a little >> adapter with a 74LS11 and a properly programmed 27C256 on it. > ------- > One of Jim Brain's 2364 adapter boards ($1.50, $5.00 assembled) is ideal > for > this; just add some diodes and a pull-up resistor to wire-AND the /CEs. > http://store.go4retro.com/2364-adapter/ I don't like the wired AND and prefer to use a logic chip since that will make sure the _CS-line for the ROM goes inactive as fast as it goes active (LOW). Watch what a pullup does to a signal on a scope and you'll see what I mean. A good example being the R/_W line on the C64 board the moment VIC uses AEC to remove the CPU from the bus. And that one has a 1.5KOhm pullup! Also, almost all 2364 to 27xxx adapters have the same design flaw, they tie _CS for the EPROM to GND and use _OE to control it. This works obviously, but it keeps the EPROM active all the time, eating power, since _OE only controls the output drivers. Unless you want to use very slow EPROMs and need the extra few ns a grounded _CS will give you, the proper way is to tie _CS and _OE of the EPROM together when connecting them to the control signal from the board. Gerrit Message was sent through the cbm-hackers mailing listReceived on 2012-05-14 17:00:35
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