Hi
I would like to use a common 12 Bit TTL counter to count from say from
100 to 1000 and start again from 100. As for know the master reset pin is used to count from 0 to 1024 but I don't have any idea to begin the count with 100 and finish it at 1000.Is there an easy way to do these or the only way is to add AND and OR gates?
Sorry about the ignorance but I don't know how to do it, any ideas would be kindly appreciated Best Regards
-- If you want to count in binary you will need three presettable 4 bit counters, like 74HC160\'s or 162\'s, but if you want to count in BCD you will need four presettable BCD counters, like 161\'s or 163\'s. In either case you will need to decode the 1000 state with external logic and use that to load the counter with 100. What is your application?
If the counter does not have parallel load, it will always count from zero (when you reset it).
To make it wrap after a count value other than 4095, yes, you need additional logic.
I would use a CPLD for that (or a microcontroller, if you don't need extremely short delay times).
Its a long time since I've done TTL, butI think you need a down counter, not an up counter. IIRC many downcounters will preload a new count when it hits zero.
Just think backwards
martin
I should have said "If the counter does not have neither parallel nor serial load, it will always [...]", but I directly discarded the cumbersome serial option.
74?160 BCD with asynchronous Clear 74?161 4 Bit with asynchronous Clear 74?162 BCD with synchronous Clear 74?163 4 bit with synchronous Clear
(If you need a glitchless power up reset, use the '160 or '161).
What he said. If you want to count from 100 (or any arbitrary number) to 999, you can simplify the decoder by using the "Ripple Carry" Outputs of three '160s (or '162s) by combinding these with a Nand gate and connecting that to the "Load" control input of the three chips, with the preset "data" inputs of the three counters set to the selected value.
Mark Zenier snipped-for-privacy@eskimo.com Washington State resident
Tiny boo boo, John. The '161 and '163 are binary. '160 and '162 are the BCD counters. Check
Of course if speed isn't needed, state machine (EPROM) counters are very versatile. GG
Make you counter count up (or down) and feed it into a ROM. The address of the ROM is the acounter values, and the data in the appropriate locations anything you wish. Reserve an output for a reset/preload. Optimise as necessarty to fit. ;-)
-- Keith
Now that I have my engineering hat back on...
Just take an appropriately sized ROM (1Kx10 bits for binary values) and register with the ROM in the feedback loop to the register. Each ROM location points to the next "state" with the final state pointing back to the first. The encoding in the ROM (count sequence) can be anything you want.
-- Keith
Hi
Thank you very much for all the great ideas. I thought it was more trivial.
The bus will be parallel loaded via a PCI interface, I was trying to check my circuit with a counter sending diferent values at some frecuency and avoid for the moment programming a PCI card but it will be better to go ahead with the PCI card
Best Regards
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