[NTLK] MP2x00 Internal Interconnect Breakout

Jake Bordens jake at allaboutjake.com
Mon Jan 5 20:28:20 EST 2015

>Serial Port 0 uses gpSerPortSel on pin 8. When gpSerPortSel switches 
>high, the card must respond with a low on DCD (5).

Did you read about this handshake somewhere or did you discover this by 
experimentation?  This possibly explains a behavior I saw on my 
oscilloscope.  When opening a serial connection (Serial0) in PT-100, the 
SerPortSel0 pin goes high for 5 milliseconds.  I thought this might have 
been some sort of reset of the LTC1323 driver.  Maybe this is the newton 
waiting for a the modem to assert DCD low?  

One thing about this case is I'm not sure how it isolates the external 
port-- for example, what happens if you've got an external modem connected 
by the external port that's asserting DCD high during this process?  You 
could do damage by having both devices trying to drive DCD.

I have to try this again and see if I see if this pulse happens when the 
DOCK application tries to access the port.  Maybe they skip this 5ms pulse 
when trying a dock connection?  I'm trying to understand how you would 
select the external port with this handshake.  IF the modem always answers 
with DCD low to this 5ms pulse, and the Newton keeps the SerPortSel0 high, 
then how do you use the external port?  We have a "use internal modem if 
available" method, but not a "use external port, even if there's an 
internal modem" method.  Not sure if I'm communicating this well.

>TVoyagerPlatform::SerialPort0LineDriverConfig(unsigned char, unsigned 
>char) writes to GPIO6 which is gpSerPortSel.

Yes, and TVoyagerPlatform::SerialPort3LineDriverConfig(unsigned char, 
unsigned char) writes to DIO 0x22... which you can also see in Ekhart's 
code.  What puzzles me here is the N2 docs don't mention DIOs greater than 
5.  I didn't realize that "2: available for configuration to the slot" 
refers to the internal modem "slot".

Unrelated: I never really paid attention to the timing diagrams in the N2 
internal slot document, but they seem to talk to how you could use an 
external clock for higher speeds.  I haven't fully parsed it, but that 
would be really cool for my use of this for WiFi.  Much better than 
115200.  Though for my current attempt, I'm sticking to standard baud 
rates.  One problem at a time...

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