[NTLK] MP2x00 Internal Interconnect Breakout
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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