Programming interface questions

Harley

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

Phil Pilgrim (PhiPi)

Harley,

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

Harley

Thanks, 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

RinksCustoms

In the begining of the prop manual it says that the prop uses these two pins to RX/TX via serial on initial powerup, after the initialization, these pins become available for general purpose. This means you can use these two pins to talk to another prop via 2-wire serial. I doubt you can program two props this way though since sync is important to communication.

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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!"

Phil Pilgrim (PhiPi)

Harley,

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

Harley

Another point:

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

Mike Green

You wouldn't need a series resistor. The 2nd Prop is an input-only and cannot provide an output on that pin so there's no possibility of having two pins both outputs, one low and one high. That's the reason for the series resistor.

Harley

Another question about this 2-Prop design......

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

Harley

Several more questions:

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