The AmG©lie project

Description: The ROM is mapped at address &F000, which in binary is %1111 0000 0000 0000. This indicates that when accessing the ROM, the address lines A12, A13, A14, and A15 will always be high. Consequently, the I/O device selections will always be active simultaneously with the ROM selection. The solution to this issue is straightforward and requires only one additional bit of logic to implement. However, it is unnecessary to add another logic gate, as the entire memory decode can be accomplished using three logic ICs, as any additional complexity would be unwieldy.

To implement the memory mapping for the ROM at address &F000, a careful design of the address decoding logic is essential. The address lines A12 through A15 are critical in determining when the ROM is selected. Specifically, these lines must be monitored to ensure that they are high, which indicates that the address falls within the range allocated for the ROM.

The memory decoding can be effectively managed using a combination of logic gates, specifically AND and NOT gates. By configuring these gates, one can create a logic circuit that activates the ROM when the address lines A12, A13, A14, and A15 are at the required high state. In addition, since the I/O devices are also active during this time, it is crucial to design the circuit in such a way that it prevents simultaneous activation of the I/O devices and the ROM. This can be achieved by incorporating additional logic gates that can selectively disable the I/O lines when the ROM is accessed.

The use of three logic ICs allows for a clean and efficient design, minimizing the complexity of the circuit. The first IC can be used for the initial address decoding, determining whether the address falls within the range of the ROM. The second IC can handle the negation of the output, ensuring that only one device is active at a time. Finally, the third IC can manage the final output signals to control the enable lines for the ROM and the I/O devices.

Overall, this approach not only simplifies the memory decoding process but also enhances the reliability of the system by preventing potential conflicts between the ROM and I/O device selections. By adhering to these design principles, a robust and efficient memory mapping solution can be achieved.However since the ROM is mapped in at &F000, this in binary is %1111 0000 0000 0000; or in other words when accessing the ROM, A12, A13, A14, and A15 will always be high. Thus, the I/O device selections will always be active at the same time as the ROM selection. Aaargh! The solution is pretty simple and would require only one more bit of logic to implement. But, it needs NOT so this would be another logic gate. I know I can do the entire memory decode with three logic ICs (anything else is just messy).