ARM microcontrollers can be clocked im several different ways. One of the ways is to use external clock with duty cycle 50-50 and a frequency range from 1MHz to 50MHz (LPC21xx series) connected to XTAL1 pin. Other way is to connect External crystal oscillator, but its range is lower (1MHz to 30MHz for LPC21xx series). And last but not least is on-chip PLL oscillator, then external clock source frequency should not exceed range from 10MHz to 25MHz. Lets analyse more deeply each clocking mechanism.

that works under Windows environment.

Another method is to use JTAG to program flash memory. This method is usually used from debugging environment. JTAG is faster than ISP – reaches up to 400kB/s.

Third method is ability to reprogram Flash memory sectors using application commands that are on chip. This feature is handy for updating code in a given sections. This is so called Field Updating.

We know that ARM MCU core can run at speed line 60Mhz or even more than 100Mhz. But usually ARM program is located in Flash memory. But flash memory execution speed can reach only up to20MHz. Practically speaking Flash memory is 3 – 4 times slower than ARM core speed can run. Of course one of workarounds could be loading critical program parts to RAM, but RAM is limited resource – we cannot locate all program to RAM as it is needed for data storing and so on. So second option is to have on chip cash memory, which stands between CPU and memory. Well LPC2000 and other ARM7 families have reduced cache module so called Memory acceleration module (MAM).

Arm microcontrollers have linear memory organisation. Starting form 0x00000000 address to 0x40000000 is Internal Flash memory location. From 0x40000000 to 0x7FFFFFFF is on chip RAM memory space. As we know manu ARM families like LPC2000 series MCU is preprogrammed with flash boot-loader and ARM real monitor debug, so both are placed at location starting from 0x7FFFFFFF to 0x80000000 memory location.