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ISP and the LPC920

Started by Dave Zendzian, December 18, 2003, 11:06:50 AM

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Dave Zendzian

Hi,

I'm currently designing the 'LPC920 into a low cost embedded application and would like to be able to perform both intial programming and field  upgrades with the device in circuit.  After reading through the device data sheets, user manuals, and the Flash Magic documentation I have a couple of questions:

1.  App note 1 suggests the use of the Keil interface circuit for use with Flash Magic.  In this circuit, Fig 7, is there a reason that RTS is connected to the R2 receiver input of IC2?  The output of this receiver is a no connect.  If there is no reason for this I could substitute a less $$ single TX,RX part.  Also, is there a reason to switch VDD to the '920 via T1?  It seems messy to have to have to power control a portion of the application circuit.  I was planning on removing this VDD switch.

2.  Is there a less expensive alternative to having to include the RS-232 xcvr, OR gate and DB connector similar to using a JTAG pod and header?  The data sheet and user manual talk about ICP programming using "5 signals and a small connector"  but I can't seem to find any more info on programmers, interface req etc.

Michael Hatscher

Hi Dave,

I do have the same problem with the ISP circuit.

If you refer to the LPC920 User Manual you will see that there is only a time window after applying Vdd to enter ISP mode.
I therefore decided to add a PNP transisor with two base resistors to Gnd and a 6pin header to my application. The rest of the circuit (MAX + HC02)goes into a 9pin/9pin case similar to my rs232-dongle (you can see a picture on http://www.elk-tronic.de/Products/DSubAdapter/RS232.htm ). Then I feed this between the PCs COM-port and the application. The pins carry Vdd+Gnd, Tx+Rx, Reset and a signal that is connected inbetween the two resistors. A high on this pin disables Vdd to the LPC, so you can enter ISP mode.

I will soon draw complete schematics on this. If you are interested please reply.

Best regards, Michael