On 10/09/2012 07:02 PM, email@example.com wrote: > > >> tAcc of an EPROM is the delay needed for the input signals to filter through the decoder, memory matrix and output drivers. (Assuming _CE and _OE are LOW) > > Does it have some sort of pipelining or does it have to deliver the data first, before reading next address? In other words for the scenario as above point [5.] is reached only after two tACCs (at most) or can it be like 1.1 tACC assuming that the last bits changed at 0.1 tACC? There is no pipelining, it's just signals filtering through the different parts and taking a certain amount of time for it. If you want you can build your own small ROM (8 Bytes). You only need a 74LS138, a handful of 1N4148 and a 74LS244. The LS138 is the decoder that selects the row, its inputs are the address lines, the LS244 is the output buffer (what you control with _OE), its 8 inputs connected to the columns which are also pulled high by weak pullups. The outputs of the LS138 and the inputs of the LS244 produce a 8 x 8 matrix. If you want a position to be read as ZERO, you put a diode there (ring towards the LS138), if you want a ONE, you leave the position empty. _OE are the 2 'G' inputs of the LS244, _CS is one of the enable inputs of the LS138. Which then will also show you the difference between _CS and _OE in the timing. (*) This little circuit, even if you build it only in your mind, should give you an idea how a ROM works and why you can change the input signals at any time and where tAcc comes from. Any change to an input pin will take tAcc before the change appears on the output pins. (*) For _CS and _OE to behave correctly, one would need an OR gate so that _CS HIGH also disables the output drivers, no matter what state _OE is in. >> The interesting signal would be to trigger on _CS going low and display PHI0 and one of the data lines and see where the EPROM output changes state and what happens before and after. > > Yes.. wondering.. maybe you could quickly wire this circuit on a breakout board (should be less than half hour) and check how it behaves on your side? I can look into it, but it will take some time since I don't have the time during the week and this weekend is also already full. Also, I know I have most parts, I'm not sure about the sockets. Gerrit Message was sent through the cbm-hackers mailing listReceived on 2012-10-09 19:00:14
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