Hi,
There is an application note for migrating from LPC2xxx to a LPC17xx devices. You could refer to AN10878 at the following link:
https://www.nxp.com/docs/en/application-note/AN10878.pdf
However, the direct pin-to-pin replacements are for LPC2300/2400. In case of the LPC2103, which has up to 32KB Flash and 8KB RAM, a low-cost replacement with same package (but no same pin distribution) and similar peripherals doubling the memory (up to 64KB Flash and 16 KB RAM) could be the LPC84x, based on ARM Cortex M0+ at 30 MHz:
https://www.nxp.com/products/microcontrollers-and-processors/arm-based-processors-and-mcus/lpc-corte...
In case of looking for a more performance MCU, you could take a look at LPC5410x MCUs, based on Cortex M4 core at 100MHz (with optional secondary Cortex M0+ core), similar peripherals, up to 512KB Flash and up to 104KB RAM, available on LQFP64 package:
https://www.nxp.com/products/microcontrollers-and-processors/arm-based-processors-and-mcus/lpc-corte...
Hope this will be useful for you.
Best regards!
/Carlos
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