[sebhc] DISKETTES and stuff

Dave Dunfield dave04a at dunfield.com
Thu Jun 3 05:34:51 CDT 2004

>> I'm not sure, but I seem to remember that the main difference between
>> the 8080 and the 8085 was that the 8085 only needed +5 volts.
>Actually, there are a considerable number of differences between the
>8080 and 8085. They aren't even close to being pin-for-pin compatible.
>About the only thing that is the same is they both have the same
>instruction set (though even there, the 8085 has several additional


The 8080 required three power supplies (+5, -5, +12), and the 8085
needs only +5.

The 8080 required a complex clock driving several lines (most people
used Intel't 8224 "clock generator"), the 8085 needs only a single
block, and can accept a directly connected crystal.

The 8080's bus is also complex, requiring the 8228 "system controller"
to obtain usable signals. The 8085 uses a simpler multiplexed bus and
ALE, requiring only a few latches.

The 8085 added four additional hardware interrupt inputs with on-chip
decoding and masking - these are the .5 vectors.

The 8085 added a pair of single-bit general prurpose on-chip I/O
signals (SID and SOD).

The 8085 got rid of the SYNC and INTE signals which made it less fun
to use with hardware front panels.

>From a software point of view, there were almost identical. There were
only two new instructions which used previously undefined opcode values.
These were SIM and RIM - to set and read the interrupt masks, as well
the single I/O bit.

It's interesting to note that the undefined opcode executed by HASL8
is RIM (0x20) - this means that it will trash the accumulator on an
8085, and therefore may NOT work the same as on the 8080.

dave04a (at)    Dave Dunfield
dunfield (dot)  Firmware development services & tools: www.dunfield.com
com             Vintage computing equipment collector.

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