Reading a Data Sheet (Help Meh!)
RICoder
Posts: 91
I have a DS1620, and I'm trying to figure out why it works perfectly with a BS2, but when I use the Prop it behaves weirdly (and it ain't my code). In that process I have come upon some questions, and they are thus:
You can find the datasheet here: http://www.parallax.com/Portals/0/Downloads/docs/prod/compshop/DS1620 Digital Thermometer Data Sheet.pdf
In the datasheet I see this (PAGE 11)
Input Resistance RI RST to GND, DQ, CLK to VDD 1M ohm
The 1M ohm is in the MIN column. Does this mean that those pins need that much of a resistor on them to work properly? It looks to me like I ought have a resistor from RST to GRN and one from CLK to VDD (which is really CLK to the pin on the chip) and one on the DQ pin to the chip. And is 1M ohm 1 MILLION ohm? What the hell kind of resistor is that?
Next question is speed of the DS1620 chip itself. I'm starting to wonder if the fact that my prop is running at 80MHz is causing issues talking to the DS1620. So, again, we look at the datasheet. (PAGE 11)
CLK Frequency fCLK DC 1.75 MHz
Where 1.75 is in the MAX column. Does this mean it cannot deal with clk pulses coming faster than 1.75MHz?
You can find the datasheet here: http://www.parallax.com/Portals/0/Downloads/docs/prod/compshop/DS1620 Digital Thermometer Data Sheet.pdf
In the datasheet I see this (PAGE 11)
Input Resistance RI RST to GND, DQ, CLK to VDD 1M ohm
The 1M ohm is in the MIN column. Does this mean that those pins need that much of a resistor on them to work properly? It looks to me like I ought have a resistor from RST to GRN and one from CLK to VDD (which is really CLK to the pin on the chip) and one on the DQ pin to the chip. And is 1M ohm 1 MILLION ohm? What the hell kind of resistor is that?
Next question is speed of the DS1620 chip itself. I'm starting to wonder if the fact that my prop is running at 80MHz is causing issues talking to the DS1620. So, again, we look at the datasheet. (PAGE 11)
CLK Frequency fCLK DC 1.75 MHz
Where 1.75 is in the MAX column. Does this mean it cannot deal with clk pulses coming faster than 1.75MHz?
Comments
You should keep the clock frequency at or below that 1.75 MHz maximum level.
Leon
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Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle
The 1M reference on page 11 is referring to the input impedance on those pins. Generally speaking, an input to any device can be a direct connection providing that the device you are connecting to has an operating voltage that is greater than or equal to the processor voltage. i.e. 3.3V for Propeller, 5V for a BS1,BS2,SX . For an output on a device, the rule is the same for an input unless there is a chance that there could be a collision between the data being sent verses data being received... i.e. bi-directional data. In such a case a current limiting resistor, usually 1K or so, is placed in series between the processors I/O and the device being controlled.
BTW the DS1620 has a voltage range from 2.7 to 5.5, so a 3.3V supply from the Propeller will work just fine.
There is an object located in the OBEX for the DS1620, but it does not tell you how to connect the chip to the Propeller.
http://obex.parallax.com/objects/search/?q=DS1620
Here are some other links.
http://forums.parallax.com/forums/default.aspx?f=25&m=147200
http://forums.parallax.com/forums/default.aspx?f=15&m=147338
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
SPAM REMOVED
Post Edited By Moderator (Aristides Alvarez (Parallax)) : 2/2/2009 1:29:15 AM GMT
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Aristides Alvarez
Education Manager
Parallax, Inc.