Content originally posted in LPCWare by starblue on Wed May 21 02:39:37 MST 2014
No, you don't need an AVR.
You need a USB-serial converter with 3.3V logic levels (I got some called FTDI Breakout).
You need to figure out the RXD and TXD pins for the serial port used by ISP from the user manual. Connect RXD of the controller to TXD of the FTDI breakout and vice versa.
Connect DTR to reset or reset the controller manually.
If available connect RTS to the pin used for entering the boot loader (look into the user manual). Otherwise set it to low manually to enter the boot loader, and high to enter your firmware.
It goes without saying that you need to connect ground.
As software for flashing use FlashMagic (MS Window) or lpc21isp (Linux).
So far the instructions is generic for LPC controllers.
On the LPC43xx you may need to check if you have to set the boot jumpers in a specific way (I'm not sure, it's been a long time since I did this.)