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Topics - amirm

#1
LPC2xxx / Minimal hardware set
October 04, 2008, 10:04:00 PM
I'm trying to learn ARM, and built a minimum hardware set.

I have 2 TQFP-64 to DIP adapter boards, with LPC2138 and LPC2148. Each board has LMxxxx regulator with stable 3v3 and 8 caps: 4 * 100nF and 4 * 1uF tantalum. Power connections are ok, I'm using 11.0592MHz crystal, set baud rate of FM to 9600, 4800.

For download I'm using a MAX232 powered at 5v - it accepts 3v3 input, with following connections:

DB9 pin2 (RX)  <--- MAX232 <--- LPC pin19 (P0.0/TX)

DB9 pin3 (TX)  ---> MAX232 ---> LPC pin21 (P0.1/RX, 5v tolerant)

DB9 pin4 (DTR)  ---> MAX232 ---> Multiturn Pot ---> LPC pin57 (reset)
the Multiturn Pot is 5k and set to output 3v3 when fed with 5v.

P0.14 is jumped to gorund.

I managed to read device signature with this setup a few times, but only after 4-5 attempts.
Now it is not working at all.
tryied both com ports of pc.they seem to be ok, tested with loopback.

looking RESET level with meter, it is 3.282V and pulses to 0.080V.

The MAX232 really works with 3v3 signals, I made a loopback with TX passing through Multiturn Pot to lower to 3v3 and sent back. ok.

Am I missing something?
Can P0.14 be left grounded all time, or do I have to control it with RTS?

Thanks in advance.