Programming interface questions
Harley
Posts: 997
I have a project that will use two Propellers. Awaiting the PDB, I am using my PropSTICK to develop code for this '16-Cog' design. I have generated a schematic for this design and several 'gray areas' have come to my attention.
1. PropSTICK schematic shows a 10K pullup resistor on the receive line (MAX3232 pin 9 to Prop pin A30). What is its purpose?____ On the other hand, the Prop Demo Board, rev C, shows no such pullup. Doesn't the MAX3232 or the FT232RQ drive the line hi/lo and not need a resistor?___
2. My 2-Prop project, I probably will need to use a PropPlug to program them. I could not find any description as to what the proper interface to a Prop should be, whether a current limiting R is necessary between the PropPlug and Prop signals. Does anyone have a schematic so one can know of this interface?
I note the PropPlug/PropClip prices have dropped!!! Thanks Parallax.
Is it correct, Tx goes to the Prop serial input pin, and Rx from Prop output pin?___ Seems bass-ackwards.
3. I was hoping to 're-use' the Rx/Tx lines after the Prop has been programmed. However, I would imagine if one leaves the PropPlug plugged in, one would NOT be able to reuse the receive line as the PropPlug would hold the output to the Stop/Idle level. Is this correct, or is there an 'open collector' output, and thus one needs a pullup resistor?___ Maybe if one had a preliminary schematic of the Prop Development Board ('soon' to be released?) this gray area would be cleared up.
Thanks for any assistance to these niggling questions.
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Harley Shanko
h.a.s. designn
1. PropSTICK schematic shows a 10K pullup resistor on the receive line (MAX3232 pin 9 to Prop pin A30). What is its purpose?____ On the other hand, the Prop Demo Board, rev C, shows no such pullup. Doesn't the MAX3232 or the FT232RQ drive the line hi/lo and not need a resistor?___
2. My 2-Prop project, I probably will need to use a PropPlug to program them. I could not find any description as to what the proper interface to a Prop should be, whether a current limiting R is necessary between the PropPlug and Prop signals. Does anyone have a schematic so one can know of this interface?
I note the PropPlug/PropClip prices have dropped!!! Thanks Parallax.
Is it correct, Tx goes to the Prop serial input pin, and Rx from Prop output pin?___ Seems bass-ackwards.
3. I was hoping to 're-use' the Rx/Tx lines after the Prop has been programmed. However, I would imagine if one leaves the PropPlug plugged in, one would NOT be able to reuse the receive line as the PropPlug would hold the output to the Stop/Idle level. Is this correct, or is there an 'open collector' output, and thus one needs a pullup resistor?___ Maybe if one had a preliminary schematic of the Prop Development Board ('soon' to be released?) this gray area would be cleared up.
Thanks for any assistance to these niggling questions.
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Harley Shanko
h.a.s. designn
Comments
I can answer the first question: The pullup is there to make sure the Propeller's serial output remains in a marking state during reset when the pins are all tri-stated. This may be important for some apps where a device is always connected to the Propeller's serial port. I keeps the Propeller from sending an errant <break> during this time. (The MAX3232's RS232 receiver input pins are pulled down, but the logic-side transmitter input pins float.)
-Phil
Ah, yes, that momentary Reset event/duration. But then, why doesn't the Demo board schematic show a pullup R?____
And if it is a problem with all situations, the PropPlug probably should include a note to pullup one or more of the lines. Sure doesn't infer any such thing in the short blurb on the Parallax web site for the part.
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Harley Shanko
h.a.s. designn
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Definetly a E3 (Electronics Engineer Extrodinare!)
"I laugh in the face of imposible,... not because i know it all, ... but because I don't know well enough!"
In devices with an FTDI USB adapter, this line is pulled up by the FT232R via an internal 200K resistor. So an external resistor is unnecessary.
-Phil
One Prop will use a 5 MHz crystal, and it will generate a 5 MHz output using FreqSynth object. This trace will be 2-3 inches from one Prop to the 2nd Prop.
Is a direct connection best, or maybe a series resistor?____
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Harley Shanko
h.a.s. designn
Each Prop will have it's own 4-pin header for a PropPlug programmer. However, the schematic presently has both of the /RST Prop inputs connected together and also the /RES pins of the PropPlug headers; only one PropPlug will be in use at any one time.
This configuration was used because there is a 'main unit' Reset switch on another board (already designed) and I planned for both Props to be reset by that signal. Does this configuration cause a problem for the Props?____ (The Reset signal has a current limit resistor (presently 10K) since it comes from 5v logic.)
Or, would it be better if Prop1 sends a 'reset' command to Prop2?___ (The two Props use FullDuplexSerial to communicate with each other.) This would delay Prop2's start by Prop1's own start up time. I would prefer the first option.
Another scheme would be to use a series resistor to each Prop and in that way isolate the PropPlug /RES signal from each other. I'd prefer using LESS rather than more Rs.
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Harley Shanko
h.a.s. designn
1. Figure 1-1 of the Prop maual, pg 17, shows four lines for a PropClip/Plug.
Once the Prop is programmed AND the programming device removed, is it OK for the Tx and Rx lines to float, or should they both have pullups?___
I've heard P30 should be pulled up so it doesn't cause some problem during initialization. Like if it is LO, it might cause a problem affecting the PC.
The /RST line when scoped is at the 3v level; apparently has a pullup internally.
2. This design is using two Props. Would it be OK for both /RST lines to be connected?___ Or would this cause a problem during programming?___
The end design will have a header for each Prop to be programmed. Would the common /RST connection be OK if even a PropPlug were on each header?___
3. Presently I am using a PropSTICK using serial COM 1 port and a DIP-40 Propeller using COM 4, using the PropPlug. Is there a way to have the PropTool 'know' which port is used when one switches between programs?___
Else the DB9 and USB pins/contacts will get quite worn out plugging and unplugging as I switch from making changes to each program and programming the associated Prop.
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Harley Shanko
h.a.s. designn