Author Topic: SBC65EC Usable Pins  (Read 3888 times)

FrozenMel

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SBC65EC Usable Pins
« on: June 21, 2012, 10:43:39 AM »
Hey,
When I got my first SBC65EC, I was messing around with it by changing the "available" pins from input to output and changing the values.  I thought I read somewhere that all the pins on the two 20-pin daughter board connectors were available for use but apparently not because they were the only pins I changed (specifically RA0-2 and RB0-2) and my board burnt out.  I was then told by the supplier that I had changed a pin that controls the Ethernet module.  But I can't find any reference to this in the documentation, or I just missed it and I will keep looking.

Can anyone verify which pins I should avoid?  Or are all the pins on the daughter board connector actually available and something was just wrong with the board?  Right now I would ideally like to use RB0, RB2 and RB4 as my I/O plus RC3 and RC4 for the I2C data and clock lines.  I would however, also like to know about the other pins in case I need to change these or expand on what I have.

Also, Can I power the board using the Pins labeled VREG and GND?  From what I understand, VREG is just the barrel connector power after the reverse voltage protection diode.

gr

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Re: SBC65EC Usable Pins
« Reply #1 on: June 21, 2012, 12:00:54 PM »
DON'T USE RB0!!

Since you are a hardware engineer you can check the schematic carefully.  RB0 goes to the ethernet chip pin 3.   And even better, read this article which already has the question you asked and the answers:

http://forum.modtronix.com/index.php?topic=1380.msg4341#msg4341

If you don't have a copy of the schematic it can also be found at the above link.

FrozenMel

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Re: SBC65EC Usable Pins
« Reply #2 on: June 21, 2012, 12:33:24 PM »
Hey,
As a hardware engineer I looked at the schematic but it doesn't line up with the revision numbers so I thought it might have changed, as they tend to unless the upgrade was mainly software.  Plus, slight modifications can change a whole lot in terms of functionality.  Also, the pin labeling changes in the v3 manual so I was getting confused.

So basically, the Pins that I see as off limits for GPIO are:
B0, B6-B7
C3-C4, C6-C7
D0-D7 (used and not available on Connectors)
E0-E7 (used and not available on Connectors)
G4 (used and not available on Connector)

For power,
VREG = Input power after Reverse Voltage Diode
VCC/+5V = Regulated 0.5A @ 5Vdc Supply

gr

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Re: SBC65EC Usable Pins
« Reply #3 on: June 21, 2012, 01:36:51 PM »
Oh - I forgot to answer the other question.  Yes, you can use the daughter board vreg and GND pins to power the board.  I've done this before.  In fact I had the board powered that way for months directly to a car battery (well I had a fuse and a .1 ohm resistor used to measure current useage).  But you need to supply more than 5 volts -  according to the specs 7V to 35V DC is allowed.

AlexKots

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Re: SBC65EC Usable Pins
« Reply #4 on: November 21, 2012, 06:27:03 AM »
While B0 is used for Ethernet communication, the web page for setting port bits as input or output includes B0 as available for input or output !!

B6 is available also but if you change it to input returns automatically to output.

If you select at system setup that you don't want a blinking LED, B6 can be used for I/O.
In that case the LED is acting as an "indicator" of B6 Status.

We have also to deal with boot time when the processor is testing connection between B6 & B7.
In that period B6 is acting as Input and B7 as Output.
B7 is transmitting some pulses to B6, and this is the way system recognizes request for safe mode.

If we must use one of B6 or B7 for I/O because we need more ports than the totaly "free", then we should use B6 as output because the external input device that is connected to it does not affect the initial testing.
And there is not any problem at safe mode.

If we must use both B6 & B7, then we should use them both as outputs. The inputs connected to them for normal operation do not affect the operation of initial testing for safe mode.
In order to protect them when we will use safe mode, we have to construct a special shorting device using a socket in place of the provided short circuit.
A resistor of 2.7K between the pins to be shorted is enough for enabling safe mode.
When B7 will be driven High and B6 as Input will monitor the signal, the voltage at B6 will be at least 2.5V, a level well above 2.0 that is required for High recognition.
When leaving boot phase and inserting in normal operation, the 2.2K will require theoretically ~1.9mA in case that one output is High and the other Low.
In case of B6 Hi and B7 Lo, then both 2.7K and the LED circuit should be driven.
The controller outputs are specified at 3mA with VDD at 4.5V and output at 3.8V.
In that case 2.7K will draw 1.4mA and the LED 2.2, totally 3.6mA.
If maximum output current is 3mA, then output voltage should be 3.3V, enough for High recognition.

Finally C6 & C7 that are used for USART can be used also if it will be not used.
We just have to remove solder that is connecting J3 and J4 jumpers and leave connections open.
Then they can be used as inputs or outputs.