The memory part of my Mark 2 system is extremely simple. There are two 32K SRAM chips (actually FRAM because I had them lying around, but there isn`t any significant difference in this application). These are selected with the logical OR of the MREQ signal and A15 (or inverse of A15 for the upper chip). Because the boot code for the Z80 is held by
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the PIC and the PIC can control the whole address bus while it holds the Z80 in reset the boot code is written to normal RAM after power-on. This provides the advantage of less decode logic, and no ROM chip, as well as allowing the whole of the memory space to be used by whatever application is running as there are no "unwriteable" regions. The actual logic I used to generate the select signals is not OR gates, as there were none of these on the board, but NAND and NOT gates as I had spare of these from various other functions. The translation is based on De Morgan`s Laws about equivalence of inverted operators. Basically if I invert both inputs and output of an and gate it becomes an or gate. However since I have a NAND gate the output is already inverted, so inverting the inputs will make the output equivalent to my OR gate truth table. This actually only requires one extra gate as I would have to invert A15 anyway, the inverted version is just used in the select for the other chip now, and the extra gate is a NOT gate on the MREQ signal. I`ve mentioned here that I`m using FRAM chips. I currently don`t plan to use them for storage of data however, as I have found them somewhat "temperamental" in home made circuits in the past. If you are interested in storing data in them through power-cycles, it`s worth noting that somewhere in the data sheet it suggests using a pull-up resistor on the chip select pin, this avoids any...
This project fits more for custom made battery casing that can have more space to hide things inside. This switch with few alterations can be used for any other project as well but is designed based on e-bike needs! This project use a clever functionality of....
The circuit described here uses ultrasonic oscillations and operates based on the propagation velocity of these oscillations in the air. Thus, we can easily determine the distance of two points if the time within which the wave travels this distance is....
Sometimes the precious metals are hidden too deep and are not detected except with complicated devices. In many cases, however, small pieces of precious metal buried near the surface can be detected by relatively simple means. Everyone is very attractive to....
Many times for various reasons we forget or can not water the plants that we have in our homes. And many humidity sensors units just notify us with a beeping sound or with a flashing light, that the pot needs watering. But what if we are away from home? This....
The principle behind a metal detector is really very simple. Proof of this is the circuit that follows, in which it proves that the construction of a metal detector can be done in the minute, with few components that we find very easily everywhere. With the....
The sub-harmonic bass generator is a sound producing unit for guitars. The sound it produces looks very much like that of the bass guitar. The octave generator is sometimes quite unusual since it does not produce any of the usual ways of coloring the sound,....
In the past the sounding (sea bottom measurement) was done with the "bullet", that is, with a heavy lead object that the seamen plucked into the sea hung from a calibrated rope. As soon as the "bullet" reached the bottom, the depth appeared directly from the....
This Amplifier was designed to have the following specifications: Distortion less than 0.1% at full power of 100W even at 20KHz. Power has to be attributed to an extended bandwidth. The output transistors must be protected against short circuits. The power....
A series of LEDs serve to alert the gardener when plants need water. Using two conventional digital integrated LEDs and a series of LEDs, we make a very useful device for gardening. The device detects the amount of water in the pot and alerts the grower.....
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