Intel clock drivers for 8085

Hey!
So, in the 82XX series peripheral/support chips for the intel processors, there are clock/ready/reset chips for both the i8080 and the 8086/8088 - the 8224 and the 8284.
But what to do with the 8085? Do you just not use one, or can one of the others be used?

Thanks!

--Christoffer

The 8085 has its own internal clock generator. You can use an external crystal, RC or LC network or external clock signal. Said input is at 2f. And that's the beauty of the 8085--you can have completely functional 2 or 3-chip systems. Bitsavers should have a ton of app notes.

The 8085 has a built in oscillator, you can connect a crystal and capacitors directly to X1 and X2. You can use a TTL clock into X1 as well. Remember, clock frequency is divided by two, so you need a 4 MHz crystal for 2 MHz operation. See the 8085 datasheet for recommended crystal types and capacitor values.

Likewise, there's no need for external ready/reset conditioning. Pretty much the only support chip you'll need is an 8-bit latch (unless you're using chips designed for use with the 8085, like the 8755 or 8155, in which case you need no external support chips, just decode logic). Part of the reason it's one of my favorite vintage processors -- so easy to interface with!

It's a shame that the world has gone Z80-mad. The 8085 was a remarkable chip, especially when considered in the light of the 8080. Single power supply, TTL logic levels, simple clock source, built-in "half interrupt" controller, even a "bit bang" serial I/O capability. The instruction set was extended, but not officially documented, so most were unaware of the extensions. If you didn't use the made-for-8085 peripheral chips, pretty much all that was necessary was to demux the address-data bus, which is no big thing. At some point, I think that Intel lost interest in it, as AFAIK, it tops out at 6MHz.

I've never used the SID/SOD pins for actual serial data, but they're a very convenient way to test your basic 8085 setup when you're building it -- I usually end up with the 8085, a latch, and a ROM as a start, and try to blink a LED on the SOD pin.

The NSC800 was even a bigger flop--probably due to timing and publicity. I wasn't even aware of it for some time. Z80 instruction set, but no bit-bang, half-interrupts and multiplexed bus. It should have made a real mark in the market, but didn't.

Well that's great news! The original MCS-85 used the SID/SOD, driven with some transistors, as a teletype interface, so it might be viable for general serial comms, if one can live without handshaking.
Wow! The NSC800 looks amazing! Never heard of that one.

There was an article way back when in one of the magazines (Kilobaud perhaps?) about replacing the 8085 on a Godbout/Compupro 85/88 board with the NSC800 to give Z80 functionality. IIRC, it wasn't very complicated; a few inverters, and perhaps a gate. Wish I could remember where that one was...

Chuck(G) said:

There was an article way back when in one of the magazines (Kilobaud perhaps?) about replacing the 8085 on a Godbout/Compupro 85/88 board with the NSC800 to give Z80 functionality. IIRC, it wasn't very complicated; a few inverters, and perhaps a gate. Wish I could remember where that one was...

Click to expand...

I believe I've seen a chunk of perfboard hanging off a CompuPro 85/88 board where the 8085 went, now I have a clue as to what it was!