Connecting a 68882

turrican

Hello,

has anyone considered to connect a 68882-FPU (at 50MHz) to the Prop?

I know that there is a "Soft"-FPU which takes a cog to calculate with Float-Numbers, but i am planning a Project
where i need as much cogs i can get

I think that the biggest Problem will be that the 68882 needs TTL-Voltage-Signals (0-5Volt) and the Prop normally
runs at 3,3 Volt... (i read already the thread about interfacing 5V-Signals to the Prop, but this handles only one
side of the Problem because 5Volts are needed as Input and Output - does anyone know if there is a bus-driver-iC
which can "translate" between the Prop and the 68882?)

Greets,

Mathias

Bergamot

I have one of these. I haven't really played around with controlling it from the propeller much, but it looks a little cheaper than the 68882, and will run on 3.3V power, which is nice.

Ale

A couple of level shifters will do the trick, more reliably than some resistors. The real challenge will be to program it , I never saw in the manual how actually it gets instructions and data. But with as little as 8 Bits of Data it should work (according to Moto manual :-D), ykmv.

deSilva

turrican said...
i read already the thread about interfacing 5V-Signals to the Prop...

Did you???

turrican

Yes, i did - but the solution with resistors seems not so suitable for this - why do you ask?

Mike Green

See en.wikipedia.org/wiki/Motorola_68881 for a description of the 68882 and how it works with a 68030 processor to do floating point. It seems like a lot of work to make this go with a Propeller. There are a variety of parts mentioned in the thread on 5V interfacing for the Propeller. The ones for interfacing I2C might work for this (like the TI TXB0104 and similar level translators).

Ale

SN74LVC4254

focus.ti.com/docs/prod/folders/print/sn74lvc4245a.html

8 Bit CMOS/TTL Bus Transceiver for dual power supply. 1$ or so each.

This manual provides a bit of information and some circuits to connect the 68882 to the 68k processors, it does not seem very complicated, not more than a T6963 LCD controller, programming is something else:

www.freescale.com/files/32bit/doc/fact_sheet/BR509.pdf

There is a register map on page 12, very light on details. May be some info survived from the Amiga days, were it was connected to a 68000 in memory map mode. That could give you a hint to how to program it. If you know how to please enlighten us. I am just curious.

edit: for comment con complexity.

deSilva

@Bergamot: Thank you for your link to the MicroMega FPU - I shall receive one during the next week and I am very, very excited to assess its power. Looks like a bargain for 20 $. I shall report a benchmark

@Turican: Sorry for my imputation. But there is a lot more in this thread than "serial resistors". I remember, I gave a link to a comprehensive "Sparkfun Tutorial" about this matter. Most interesting using a diode in combination with a pull-up resistor.... But when neeeding really fast AND bidirectional connections, professional level shifters might be best...

turrican

@deSilva: This was my oppinion too...

I have a very good book from my "old" days when i was designing and programming hardware/software-stuff for the Amiga-Computers, its named "MICROPROCESSOR SYSTEMS DESIGN, 68000 Hardware, Software and Interfacing" - its a very good book about building complete 68k-based systems from the 68000 to the 68060 even with the MMU and FPU-things. So based on this informations about the hardware AND (what is even more important to me) the software i want to connect the 68882 to the prop.
I will have a look at the CMOS-TTL-Bus-Transciver, maybe it is suitable for this application!

Thanx for you replies!