PC ROM emulator circuit

This ROM emulator improves the easiness to build/use it by reducing down its function which can be used as a ROM emurator. The kind of the ROM types to be emulated, are 2764, 27128 and 27256. The debugging capability is only Load and Run, omit functions such as trace or step execution. It will still sufficient because Load and Run is used mainly even if using an ICE. No power requiment. Operating power is supplied from the target system. However, the data on the buffer memoly is not held when the target power is down. Therefore, the data must be sent again after power is up. Use a PC to control the ROM emurator via a parallel port instead of an interface board to attach it to the various PCs easily. Build the ROM emulator as small as possible. Let's try a limit of the miniaturization this time, the card size is a goal.
PC ROM emulator circuit - schematic

Because a goal is card size, all the parts to be used are surface mount devices. All parts are mounted on the settlement side of the proto-board of 50mils pitch. First, after the position of the ICs is decided, wire in the order of the power line and the signal line. It is good when TA(0.5mm dia) is used for the power lines and UEW(0.2mm dia) is used for the signal lines. Wire signal lines as route between the IC's. The wire is connected with pre-soldering because it cannot be wound to the lead of the ICs. Be careful because it becomes the end and has difficulty if it isn't wired with thinking about the wire density. When wiring is finished and operation is confirmed, cover the circuit board with thin plastic board. The part inside dashedline of the circuit diagram could be built within the size of 69mm x 47mm x 5mm as a result of the try to the miniaturization. The goal was decided to be attained with ease because it was card size. The power lines that signal returns, of the connection cable from the ROM emurator to ROM plug, are only two. You had better shorten it as much as possible. There was no special part in the junk box, I used only standard logics. When you couldn't obtain SOP ICs, DIP ICs can be used. I recomment to use DIP ICs instead of SOP ICs. When PROG signal goes "Low", the ROM emulator enters Running Mode. The address from the target system is inputted to buffer RAM via U3 and U4. The read data from...

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