All About Jake

Eckhart Köppen, author of the Blunt, the Newton bluetooth stack, has posted code on GitHub for manually controlling the SerPortSel3 signal.  His code manually controls the proper DIO pins using functions in the Newton ROM.

0x0026d050 SerialPort0LineDriverConfig__16TVoyagerPlatformFUcT1
0x0026d094 SerialPort3LineDriverConfig__16TVoyagerPlatformFUcT1

I took a look at the assembly for these functions and found them to be pretty simple.  The first parameter seems to be a boolean and the second a bitfield.  I’m not exactly sure what the second parameter does, but it changes the behavior of the function when it finds the 0x20 bit set.

From what I can tell, for the Port3 function, you can leave the second parameter as 0x0 and the first parameter is a bool that controls the signal.  For the Port0 function, the first parameter the logical inverse of the signal you want, and the second parameter should be 0x20.

• SerialPort0LineDriverConfig(0,0) // results in Port0Sel High 
• SerialPort0LineDriverConfig(1,0) // results in Port0Sel High 
• SerialPort0LineDriverConfig(0,0×20) // results Port0Sel High 
• SerialPort0LineDriverConfig(1,0×20) // results Port0Sel Low 

• SerialPort3LineDriverConfig(0,0) // results in  Port3Sel Low 
• SerialPort3LineDriverConfig(1,0) // results in Port3Sel High 
• SerialPort3LineDriverConfig(0,0×20) // results in Port3Sel Low 
• SerialPort3LineDriverConfig(1,0×20) // results in Port3Sel Low

Eckhart’s code is an awesome blueprint for calling arbitrary memory locations, so it was easy to modify it to call these two functions.  Putting it all together, I whipped up this little Newton application:

Still a little more work to do, but good enough for development and testing.

Incidentally, when called with the correct parameters, the assembly behind SerialPort3LineDriverConfig is virtually identical to Eckhart’s code.  The SerialPort0LineDriverConfig is very similar but uses as GPIO instead of DIO.

The internal serial port of the Newton MessagePad 2×00 exposes the same ports as the external interconnect.  In order to prevent two devices (one internal, one external) from diving the port at the same time, there are “Serial Port Select Pins” for Serial Channel 0 and Serial Channel 3.

Pin 1 PortSelect:
This is the control signal to select between a  peripheral in the internal Serial SLot and the Newton Interconnect Port.  When the signal is low, the Newton Interconnect POrt may drive the Serail Port 3 Signals.  When the signal is high, the Internal Serial Slot Peripheral may drive the Serial Port 3 Signals.

Pin 8 gpSerPortSel
This signal controls the LTC 1323 line driver for Serial Port 0 that drives the 26 pin Newton Interconnect Port.  When Low, the Newton Interconnect Port can drive Serial Port 0.  When high, the internal Serial Device can drive serial port 0 on the 32 pin connector.

I seem to have an odd, recurring interest in the internal serial port on the MP2x00.  A few years back I tried to make an internal bluetooth module.  It worked, but I never got the RF design correct so it didn’t work well.

Now, I’d like to try for an internal WiFi module.  I’m more hopeful that I can get the antenna correct by using more off the shelf components and, worst case, an external antenna.

The internal port was originally designed for an internal modem that was never produced.  Luckily, some of the design documents were leaked and are now available.  The documents give you part of the picture, but there are omissions and errors that make the process a bit more of an exercise in reverse engineering.

I wanted a breakout board that would help prototype and test the behavior of some of the GPIO pins and such.  I came up with this:

The connector is a FTE-116-01-G-DV-ES.  It is easier to find without the -ES option, FTE-116-01-G-DV-P for example is available from Newark electronics.  The ES is just an end shroud, which while a nice thing, is not strictly necessary.  I think the pins are a little longer than the original JAE connector, so it sits a little high.  The case seems to close so I’m hopeful that it’ll work for an internal card as well.

I had 20 of these boards made for $15.  You’ll have to solder the connector on there yourself, but if you’re playing around with this sort of thing, you probably know how to handle surface mount pins of this size.