Multiple DS1620 one Stamp

Hulk

I'm new to 3-wire comunications, but some research indicates that I could use a single Pin on the stamp to connect to (for instance) the DQ i/o pins of two DS1620 chips and that I could connect another single pin of the stamp to the CLK pins of the two DS1620 and then "strobe" the RST (not) line to each individual DS1620 to discriminate between the two temperature inputs.

When I look for information on 3-wire I've found statements like "all pins can be tied together with the exception of CS (chip-select)".· I have to assume that the RST(not) line is the equivalent of chip select.

I may have as many as 4 DS1620s connected to a stamp; will the pin designated to send signals to the CLK input have sufficient fan out to drive the DS1620s in my scenario?

Any guidance is appreciated.

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Mike Green

You could certainly connect one Stamp to 4 DS1620s by tying all the CLK pins to one Stamp I/O pin and all the DQ pins to another Stamp I/O pin. Each of the RST/ lines would have to be connected to a separate Stamp I/O pin. The maximum fan out for a Stamp I/O pins depends on how fast you plan to drive the I/O lines and the total capacitance of the lines. The I/O pin circuitry has an effective resistance and that, combined with the load capacitance (all the DS1620 pins plus the circuit board capacitance) slows down the signal changes (edges) and that puts an upper limit on the switching speed. The Stamp and its SHIFTOUT and SHIFTIN instructions are relatively slow and you can probably drive all the DS1620s that you have pins to select given the 16 I/O limitation of most of the Stamps.

Hulk

Thanks Mike!
Exactly the information I need.

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Mike Green

When you do hook things up, be sure to include pulldown resistors on the RST/ leads. You want to be sure that the unselected DS1620s are held in reset, particularly when the Stamp is reset, before your program has a chance to initialize the I/O pins.

Hulk

Do you think 2k is low enough to drag it down or do you have a better recommendation? BTW thanks for staying with me on this as I might have chased shadows without your suggestion!

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