If I understand you correctly then Bob you would have to input from the port twice ? First to setup the output (low to high on pin 21), then AGAIN on another output pin (say pin 22) which would be connected to the CLK pin1. This would clock the register from the first output. That output would fee into pin 23 so it can be inverted next time. If I have this correct, it’s not really what I want. I need one input from the port to toggle. Otherwise I have to backtrack on old software. If I have it wrong could you supply PALASM code and/or a diagram. I’m attaching the current schematic. I would like to eliminate the need for the 74LS74. Thanks John From: n8vem...@googlegroups.com [mailto:n8vem...@googlegroups.com] On Behalf Of Bob Bell John, I’m just beginning to get into programming GALs for an S-100 memory board I’m designing (or I should say re-designing), and I have been doing a lot of research. In the 80’s, I used PALASM to program PALs on a regular basis, so my need to learn GAL programming is awakening many old memories. If I understand you correctly, you want a GAL output to start low (upon some reset or power-up I presume), then on an input from port 00EDh, you want it to go high and stay high. Then on a subsequent port input, you want it to go back low and stay low. As I see it, this is a simple divide by two circuit. If I was implementing it with a D flip-flop, I would simply tie the /Q output pin back to D input and then clock the flip flop with the output of the port detection logic. Assuming you want a known state on power-up or reset, I would connect the D flip-flop’s /Reset input to /POR. So, for your GAL, you’ll need a registered output. Since a 22V10 has a single, common clock input, and cannot come from the matrix or a GAL output internally, you’ll need to tie that to another output that has implemented your port detection logic as you have written. Then each time you write to that port, the GAL combinatorial logic will pulse its output and be fed back to the clock input, clocking the register cell that you will setup. Your port detection logic looks correct to me. This would be the combinatorial output that you will wire to the GAL CLK input. Then you need to add an equation for the registered cell that uses the output of the register, internally, to set the register output either low or high depending on the state of the register output feedback. This will implement the toggle function you are looking for. That would look something like this I think: TogOut = /TogOut So, I think you have enough pins. The output of the port detection logic can be pin 23. This is hard-wired externally to the GAL to pin 1. Since the register output can feedback internally, it does not use a pin. That leaves pin 22 for your reset if you want to implement that. I know this is not thought out 100%, but I hope it’s enough to help you get going. Bob Bell From: n8vem...@googlegroups.com [mailto:n8vem...@googlegroups.com] On Behalf Of monahanz Could anybody out there that remembers programming GAL's (specifically the 24 pin 22V10 variety), help me on what I'm sure is a simple problem. I want the GAL to topple low to high on a port input. and stay high., The next time on a port input toggle back high to low and stay low. In other words inputting from a port toggles the output. I'm a bit limited with pins available, only 3:- PIN 1 NC Pin 13 A10 Pin 23 NC ;----------------------------------- Boolean Equation Segment ------ EQUATIONS TOGGLE_OUTPUT = A0 * /A1 * A2 * A3 * /A4 * A5 * A6 * A7 ;EDH = 1110 1101 I'm assuming I need a register output, not sure what the clock should be. Any suggestions as to a layout. John -- -- |
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