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How to Start hardware of 8085up......??
- Thread starter RITESH
- Start date
I see. While technically feasible, using an 8085 to update/refresh (through some non-trivial driver circuitry) a very large array (many thousands?) of LED's will make for one really poor TV i.e. up to ~30 seconds per frame update, as opposed to 25 frames per second minimum for a real TV. You would need alot more 'video bandwidth' than an 8085 can directly provide..
Probably a more practical application for an 8085-based system would be something like a 50 x 8 LED 'moving message' display, IMHO.
Regards Valentin
PS: This thread, while interesting, isn't specifically about 'IBM-PCs and compatibles'? I vote that it be moved to a more appropriate section of the VC forum (though I suppose the same could even be said of my own project thread, heh..:D).
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glitch
Veteran Member
They should be available through most mail order or online parts suppliers. If nothing else, eBay usually has large quantities of 2864/2764 available cheaply.
eeguru
Veteran Member
Even a PIC is serialized. You have about 80ns a pixel at SD res. And about 13.5ns a pixel at HD res. It's hard to find a MCU solution that can get a whole lot done in that time w/ zero jitter. You could certainly put a lot of MCU's in parallel, but usually digital video processing circuits use much simpler linear parallel logic either in a ASIC or PLD controlled by a CPU. Though I've seen an increasing number of ARM A3s lately with Bt.656 video input and output; mostly from Epson and NXP. Some with scaling and mixing. That would sure help a small design. But the technology difference between that and an 8085 is about 30 years! As basman mentioned, an LED message board is a more reasonable target for your next step.
eeguru
Veteran Member
You can get Atmel AT28C64's here. Those are 8 KByte Flash based EEPROM replacements. If you need more storage, you can also get Atmel 64 KByte EEPROMS here. Many other suppliers also sell them all over the world.
per
Veteran Member
Any kind of parallel ROM chip will work, given it uses 8 data lines, address lines, and controll signals. The 27/28xx series just turns out to be the most common programmable/ereasable ROMS.
Chuck(G)
25k Member
You didn't give us much to go on.
If you have a timer circuit (e.g. an 8253) as part of your setup, the answer is easy--simply program a counter in the timer to interrupt after a specific number of counts. It's very precise and requires almost no CPU time.
Otherwise, you set up a CPU loop to count. The exact value of the count that you start with may have to be determined experimentally, but a very close estimate can be gotten simply by timing each instruction in the loop and computing how many iterations would be required. The 8085 is a very simple processor which should lead to fairly accurate estimates.
If you have a timer circuit (e.g. an 8253) as part of your setup, the answer is easy--simply program a counter in the timer to interrupt after a specific number of counts. It's very precise and requires almost no CPU time.
Otherwise, you set up a CPU loop to count. The exact value of the count that you start with may have to be determined experimentally, but a very close estimate can be gotten simply by timing each instruction in the loop and computing how many iterations would be required. The 8085 is a very simple processor which should lead to fairly accurate estimates.
Chuck(G)
25k Member
I don't believe that a Z80 is any more accurate regarding timing than an 8085--at least I can't see any inherent reason. I'd be interested to hear his reasoning--and be given a chance to rebut it if I think it's faulty. It could simply be that he's not familiar with the 8085. Does he think that an NSC800 would be more accurate than an 8085, for example?
per
Veteran Member
To my knowledge, both the Z80 and 8085 uses a fixed time to fetch and execute each instruction. The timing-uncertainty of independent fetching/execution units were not introduced before the 8086. I have not done any in-depth research on this, so I may well be incorrect.
Chuck(G)
25k Member
Well, not in the x86 line anyway. Functional units, pipelining and instruction caches go back to the 1960s. Still, if you understood the CPU, it was possible to time things quite accurately. I spent many happy hours hand-timing CDC 6600 code.
After all, a CPU is deterministic. You just have to know the rules.
After all, a CPU is deterministic. You just have to know the rules.
I am wondering why you're so keen to know the answer to this? Is your school assignment question (generating 1-second delay using 8085 CPU) due to be handed in soon?
Do you have access to a copy of Intel's MCS-85 user's manual? If so, I would suggest reading through all of it (which you will have to do anyway if you're building an 'LED TV') and then kindly tell us how you would write that 1-second delay routine..
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